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COLUMBIA  UNIVERSITY 

THE  LIBRARIES 

Medical  Library 

AN  ESSAY 


ON 


mm  ©iiiaifif 


OF 


ANIMATED  MATTER. 


BY  JOHN  PATTEN  EMMET. 


"  Bene  scire,  est  per  causas  scire. 


NEW- YORK: 

PRINTED  BY  C.   S.  VAN  WINKLE, 
Printer  to  the  uuiversity. 

1322. 


M*  COLLECTION 


/P£Z 


ay 
i 


CD  an 

2 


Kif*tt0tttr*l  Wiftmvmitm 

ON  THE 

CHEMISTRY 

OF 

SUBMITTBD 
TO  THE  PUBLIC  EXAMINATION 

OF  THE 

TRUSTEES  OF  THE  COLLEGE  OF  PHYSICIANS  AND  SURGEONS 
OF  THE  UNIVERSITY  OE  NEW-YORK, 

WRIGHT    POST,    M.  D.    PRESIDENT, 

FOR  THE 

Degree  of  Doctor  of  Medicine, 

On  the  2d  day  of  April,  1822. 


TO 


WILLIAM  J.  MACJVEVEJV,  M,  U>» 

PROFESSOR  OF  CHEMISTRY  IN  THE  UNIVERSITY  OF 
THE  STATE  OF  NEW-YORK. 


Dear  Sir, 

It  is  with  pleasure  I  avail  myself  of  this 
opportunity  to  express  my  gratitude  for  the  steady 
interest  which  you  have  always  shown  in  my  behalf. 
Prompted  by  your  example,  and  guided  by  your 
instructions,  I  have  enjoyed  opportunities  of  which 
very  few  indeed  can  boast ;  and  it  shall  ever  be  my 
study  to  profit  by  them. 

Accept,  dear  sir,  the  dedication  of  this  essay,  and 
regard  it,  though  inadequate,  as  a  pledge  of  sincere 

esteem. 

THE  AUTHOR. 


288804 


THE  CHEMISTRY  OF  ANIMATED  MATTER 

/ 


DIVISIONS. 

I.  Introduction,          .  From  page  9  to  14 

II.  Chemical  Agents,           .        .         .        .  14  to  73 

Influence  of  Vital  Functions,  (page  32) 

Fluidity,  (34) 

Temperature,  (36) 

Galvanism,  (38) 

Light,  (55) 

Atmospheric  Air,  [Oxygen,]  (60) 

Alteratives  in  General,  (67) 

III.  Sanguification, 73  to  94 

Digestion,  (74) 

Respiration,  (90) 

IV.  Assimilation, 94  to  125 

Composition  and  Figure,  (95) 

Animation,  (HI) 


Digitized  by  the  Internet  Archive 

in  2011  with  funding  from 

Open  Knowledge  Commons 


http://www.archive.org/details/essayonchemistryOOemme 


THE 


©MaffiiMmT 


OF 


ANIMATED    MATTES. 


FIRST    DIVISION 


INTRODUCTION. 


There  is  no  subject  for  reflection  so  interesting  to  man 
as  the  principle  of  his  existence.  Whether  we  regard  it 
in  a  moral  point  of  view,  or  in  connexion  with  the  healing 
art,  the  most  important  advantages  must  follow  the  inqui- 
ry into  life.  Yet  it  is  a  singular  truth,  that  no  subject  has 
met  with  a  less  candid  investigation. 

Whatever  may  have  been  the  sources  of  this  neglect, 
there  seems  to  be  abundant  proof  that  no  more  designed 
mystery  is  thrown  around  this  form  of  creation,  than  any 
other.  We  have  seen  the  lightning  of  Heaven  subdued, 
Heaven  itself  scrutinized  by  the  astronomer,  and  the  infinite 
spaces  of  its  planetary  orbs  brought  to  the  level  of  a 
school  boy's  eye.  Earth  has  been  dissected  by  the  busy 
hand  of  man  ;  her  magnitude  is  measurable,  her  stores  tan- 
gible and  her  general  economy  visible.  Even  man,  who 
proudly  raises  his  head  above  the  range  of  creation  and 
styles  himself  its  lord,  meets  with  as  humble  an  analysis. 

3 


10 

His  life  is  sustained  by  the  same  principles  as  that  of  the 
brute  or  plant ;  and  the  fabric  which  gives  him  his  supe- 
riority moulders  into  the  common  stock  of  matter  which 
has  served  him  and  others  since  creation.  All  created 
beings  are  members  of  one  and  the  same  family,  and  every 
day's  examinanation  teaches  us,  that  distinction  is  but  in 
degree.  "  The  more  the  phenomena  of  the  universe  are 
studied,  the  more  distinct  their  connexion  appears,  the 
more  simple  their  causes,  the  more  magnificent  their 
design,  and  the  more  wonderful  the  wisdom  and  power  of 
their  author."  How  does  it  happen,  then,  that  with  all 
this  similarity  and  connexion  throughout  creation,  the 
principles  of  animation  should  be  pressed  down,  as  it 
were,  into  darkness  ? 

It  has  often  been  asserted,  that  to  inquire  into  the  na- 
ture of  our  vitality  is  to  go  much  farther  than  ever  the  Crea- 
tor of  life  intended.  This  conjecture  (for  so  it  is  at  best) 
has  gained  too  easy  a  reception.  Man  is  a  rational  being, 
and  stands  pre-eminently  distinguished  above  all  other 
animals.  This  superiority,  at  first  sight,  seems  to 
leave  between  him  and  them  nothing  in  common,  and 
has  hastily  led  to  the  conclusion  that  the  principles  of  his 
existence  are  of  another  nature,  and  too  refined  to  be  com- 
pared with  that  of  the  brute.  A  review  of  animated  be- 
ings shows  how  ill  founded  such  an  opinion  is.  It  may 
be  just  as  to  man's  superiority  in  the  complication  of  his 
living  powers,  but  cannot  give  any  thing  like  a  founda- 
tion for  supposing  a  peculiarity  of  principle.  It  will  be 
found,  that  the  perfection  of  organization  is  always  fol- 
lowed by  a  proportional  perfection  of  life,  in  all  animals 
alike,  and  that  in  man  himself  its  progress  is  intimately 
dependent  upon  the  state  of  his  structure,  during  every 
period  from  his  infancy  upward.     In  what  other  light 


11 

can  we  consider  the  life  of  an  infant  than  as  animal  lifes 
such  as  the  offspring  of  animals  are  universally  endow- 
ed with  ?  If  intellect  at  the  same  period  of  existence 
is  to  be  considered  as  a  just  criterion,  surely  we  cannot 
place  the  infant  in  comparison  with  the  chicken  or  the 
calf.  Metaphysical  reasoners,  who  have  built  their  ar- 
guments upon  a  subsequent  superiority  of  mental  faculty, 
have  overlooked  the  formations  of  education.  It  is  no  less 
absurd  to  suppose  that  the  human  faculties  previously 
existed,  and  were  only  developed  by  age,  than  to  suppose 
that  all  the  infinite  number  of  human  forms  which  have 
appeared  since  the  creation,  and  are  to  appear  hereafter, 
were  originally  incarcerated  together  in  the  same  original 
ovarium.  No  argument  can  be  drawn  from  the  mental 
faculties  without  consulting  their  origin.  Abstract  ideass 
and  the  force  of  recollection,  are  by  no  means  more  in- 
conceivable than  the  operation  of  will,  in  consequence  of 
those  ideas ;  yet  the  brute  has  this  last  faculty,  in  some 
degree,  as  well  as  man.  A  cow,  for  instance,  whose  head 
is  turned  away  from  the  barn,  will  sometimes  suddenly 
rise  up  and  go  directly  toward  it,  though  the  place  she 
has  left  should  be  covered  with  provender,  and  external 
impressions,  as  the  weather,  &c,  apparently  more  favoura- 
ble to  her  remaining  where  she  was.  In  this  case,  the 
abstract  idea  seems  to  occur  in  the  same  manner  as  with 
ourselves.  So,  also,  we  find  watch  dogs  suddenly  spring 
from  their  sleep  and  bark  furiously,  when  there  is  no  ex- 
ternal impresssion  given  to  the  ear  or  other  parts  of  the 
body  :  other  dogs,  of  the  hunting  kind,  will,  also,  during 
sleep,  howl  as  they  are  used  to  do  in  the  chase.  We  can- 
not attribute  these  acts  to  any  other  than  abstract  ideas  ; 
we  know  we  frequently  have  such  passing  within  our- 
selves during  sleep;  and  we  cannot  attribute  their  ap- 


12 

pearance  to  habit.  If  habit  could  make  the  dogs  bark, 
the  more  powerful  one  of  walking  should  prevent  them 
from  lying  still  any  length  of  time.  Numerous  instances 
of  abstract  ideas  could  be  pointed  out  among  the  inferior 
animals  ;  but  a  few  are  sufficient  to  show  the  probability 
of  more.  Now,  the  conclusion  fairly  to  be  drawn  from 
such  facts  is,  that  where  there  are  abstract  ideas,  there 
must  be  reason  ;  depending,  as  to  its  perfection,  upon  their 
number.  Here  we  must  observe  a  similar  constitution 
between  man  and  brutes.  Memory  also  has  the  same 
foundation  in  one  case  as  the  other.  The  power  of  re- 
cognition is  even  more  manifest  in  some  brutes,  and  the 
faculty  of  committing  to  memory  is  as  strikingly  illustra- 
ted in  the  instances  of  birds,  when  they  whistle  without 
interruption  the  tune  which  they  first  heard  from  a  hand- 
organ,  as  it  is  in  man  under  similar  circumstances.  It 
is  gratuitous,  to  suppose  a  difference  of  principle ; 
and  man,  though  towering  in  his  wisdom,  may  yet  go 
through  the  fields,  and  receive  a  lesson  from  the  ant  or  bee. 
Whatever  may  have  been  the  feeling  which  dictated  the 
distinction  between  reason  and  instinct,  we  cannot  but 
perceive  their  resemblance,  and  acknowledge,  that  their 
difference  lies  only  in  degree,  and  is  dependent  upon  or- 
ganization. Another  consideration  leads  us  to  view  the 
principle  of  life  as  similar  in  both,  and  as  depending  for 
its  existence  upon  the  body,  without  possessing  a  separate 
character.  Man  and  brutes  receive  their  original  ideas 
from  external  impressions  ;  such  are  those  of  light,  colour, 
figure,  taste,  smell,  dimension,  hardness,  warmth,  &c. ; 
their  combination  which  afterwards  helps  to  inform  the 
mind,  must  therefore  be  considered  as  dependent  upon  the 
material  organs,  which  first  gave  the  impression.  Fur- 
ther, the  capacity  to  receive  these  ideas  follows  the  per- 


13 

fection  of  organization  through  all  its  varieties.     When  th£ 
bodj  suffers  from  disease,  the  mind  fluctuates,   and  when 
the  corporeal  fabric  ceases  to  exist,  so  must  the  principle 
of  life,  whether  its  maturity  be  instinct  or  reason.    Where 
then  do  we  see  any  superiority  over  the  brutes,  as  to  a 
difference  of  vital  principle  ?     I  cannot  perceive  a  single 
circumstance  to  make  the  inquiry  into  man's  existence  or 
generation  in  the  least  degree  more  improper  than  one 
into  that  of  the  oyster,  sea-nettle,  or  fungus.     The  com- 
mencement of  animation   is  as  wonderful  in  one  part  of 
creation  as  in  another ;  all  show  an  invariable  dependence 
upon  the  same  principle,  and  are  equally  the  works  of  one 
Creator.     It  is  singular  how  much  is  overlooked  in  trying 
to  hold  the  veil  over  life,  and  particularly  over  that  of  man. 
We  give  it  independence   without  being  able  to  strike  off 
its  weakest  shackle  ;  and  have,  in  the  end,  to  leave  it  as 
our  conformation  requires  it  to  be — a  consequent  of  ma- 
terial composition.     If    the   inquiry  be  improper,  why  is 
not  the  practice  of  physic  considered  as   an  audacious  at- 
tempt to  pry  into  forbidden  secrets?     Why  are  not  anato- 
my and   physiology  ?  The  last,   in  particular,    aspires  to 
develop    the    sources  of  life.      We    even    applaud    the 
ingenuity  of  physiologists,  when  they  attempt  to  introduce 
physical   laws  into  the    economy   of  the  animated  body. 
The  reason  plainly  is,  that  the  view  of  life,  as  generally 
entertained,  is    unfounded ;    for   what   is    considered   as 
a  distinct    principle   is   nothing    more   than   an    effect, 
and  its  regeneration  takes  place,  day  after   day,  in    as- 
similated  nutriment.     For   these   reasons,   I   shall    con- 
sider  the   production   of  all   organized  matter  (whether 
animal  or  vegetable)  under  the  same  light,  and  as  I  can- 
not see  any  assignable  difference  in  their  principles  of  life, 
I  shall  not  assume  one  ;  but  enter  upon  my  subject,  trusting 


14 

that  all  knowledge,  which  is  founded  upon  observation  and 
experiment,  must  be  proper ;  since  otherwise  I  conceive 
the  light  for  investigation  would  have  been  withheld. 

SECOND    DIVISION. 

I.  THE  POWER  OF  LIFE. 

Man  has  been  early  taught,  by  observing  the  uniform 
results  of  putrefaction,  that  the  living  structure  is  com- 
posed of  the  same  materials  as  constitute  the  inanimate 
world,  or,  in  other  words,  that  he  is  literally  formed 
from  the  sod  under  foot.  This  humiliating  analysis  of 
nature  has  been  invariably  corroborated  by  the  more 
limited  power  of  art.  After  such  a  lesson,  it  appears 
astonishing  how  it  could  be  denied,  that  physical  laws 
have  given  us  birth.  It  is  true,  the  production  of  living 
matter,  as  we  daily  see  it,  is  accompanied  with  the  ener- 
gy of  life  in  the  whole  body;  and  this  close  connec- 
tion has  given  rise  to  a  confusion  between  the  cause  and 
effect.  When,  however,  we  consider  that  no  power  of 
life  could  draw  together  the  particles  of  matter,  or  make 
ihem  cohere  or  change  their  properties,  we  must  inevita- 
bly come  to  the  conclusion,  that  the  animated  matter  de- 
rives its  distinguishing  character  altogether  from  physical 
laws,  and  that  life  is  but  a  consequent.  To  illustrate  this, 
let  us  examine  the  vital  power  as  it  appears  after  such 
formation.  "  The  idea  of  life,"  as  Cuvier  remarks,  "  is 
one  of  those  general  and  obscure  ideas  produced  in  us  by 
observing  a  certain  series  of  phenomena  possessing  mutual 
relations,  and  succeeding  each  other  in  a  constant  order. 
We  know  not,  indeed,  the  nature  of  the  link  that  unites 
these  phenomena ;  but  we  are  sensible  that  a  connexion 


15 

must  exist,  and  this  conviction  is  sufficient  to  induce  us  to 
give  it  a  name,  which  the  vulgar  are  apt  to  regard  as  the 
sign  of  a  particular  principle,  though  in  fact  that  name  can 
only  indicate  the  totality  of  the  phenomena  which  have 
occasioned  its  formation."  According  to  this  correct 
view,  whenever  we  consider  life,  we  shall  find  its  investi- 
gation inseparable  from  the  corporeal  system  in  which  it 
exists.  We  know  that  it  depends  upon  the  mutual  exer- 
cise of  material  organs,  which  are  liable  to  be  acted  upon 
by  external  agents,  or  decomposed  like  other  matter. 
The  metaphysician  and  divine  may  show  its  importance, 
by  connecting  it,  in  their  discussions,  with  the  soul  ;  but  the 
little  knowledge  that  we  have  on  that  subject  bewilders 
the  conception,  though  it  may  not  shake  the  faith.  Life, 
as  we  have  it  before  our  eyes,  is  nothing  else  than  the 
aggregate  effect  of  numerous  material  organs,  endowed 
with  an  irritability  which  subjects  them  to  be  constantly- 
stimulated  into  peculiar  and  appropriate  actions. 

The  physician  who  wishes  to  support  or  recruit  life, 
must  give  all  his  skill  to  the  disordered  organs ;  for  the 
affections  of  these  alone  are  found  to  be  the  sole  causes 
of  disease.  In  no  instance  is  life  found  to  exist  without 
the  organization  of  matter,  and  all  its  varieties  are  referri- 
ble  to  the  same  state.  When  a  member  of  the  body  re- 
ceives an  extensive  injury,  it  may  mortify ;  and  there  is 
sufficient  reason  why  it  falls  off,  or  has  a  line  of  separation 
between  it  and  the  uninjured  part,  without  supposing  a 
vital  repulsion.  When  an  extraneous  substance  is  lodged 
in  any  part  of  the  body,  what  can  be  more  unmeaning 
than  to  say,  that  the  consequent  inflammation  is  an  effort  of 
nature  to  throw  it  off?  The  reason  why  these  expres- 
sions are  improper  is,  that  they  give  the  opportunity  for 
supposing  life  a  peculiar  intangible  spirit  and  because 


16 

they  do  not  sufficiently  imply  how  much  the  vital  organs 
are  susceptible  of  being  affected  like  inanimate  matter. 
The  great  distinctive  character  seems  to  be  the  irritability 
which  the  former  possesses  in  such  an  eminent  degree. 
But  this  property,  so  far  from  acting  the  guardian  part  of 
a  medicatrix  upon  all  occasions,  very  often  leaves  the  li- 
ving fibre  exposed  to  the  worst  of  dangers  from  decompo- 
sition, as  may  be  seen  in  all  cases  of  inflammation.  When 
we  examine  the  living  body,  we  will  find  that  one  prin- 
ciple characterizes  all  its  parts  :  this  principle  is  irritabili- 
ty, which  is  as  peculiar  in  its  nature  as  the  texture  to  which 
it  belongs.  Thus  we  know,  that  every  part  of  the  body 
can  be  stimulated  to  inflammation,  although  the  irritability 
of  muscular  fibre  cannot  be  made  manifest  to  the  sight. 
We  will  find  that  connecting  organs  are  placed  in  every 
living  part,  for  the  purpose  of  concentrating  their  powers 
of  life,  and  nourishing  them.  The  first  office  is  performed 
by  nerves ;  the  second  by  arteries  and  veins.  From  both 
we  learn  a  plain  fact,  namely,  that  the  life  of  any  single 
part,  though  the  true  type  of  animation,  is  nothing  by  it- 
self, and  that  its  power  is  insufficient  to  its  own  support. 
The  parts  of  the  body  thus  intimately  connected  together, 
readily  co-operate,  and  constitute,  by  their  amount  of  ac- 
tion, the  phenomena  of  life.  But  even  after  taking  the 
most  favourable  survey  of  this  complicated  machine,  we 
cannot  avoid  concluding,  that  its  life  is  but  a  physical  effect. 
The  property  of  irritability  has  no  existence,  unless  when 
a  stimulus  be  present ;  consequently,  although  any  part 
should  be  capable  of  this  excitement,  yet,  where  no  stimu- 
lus is  concerned,  it  is  completely  dead ;  and  further,  when 
this  property  is  manifested,  it  must  always  be  the  result 
of  action  between  two  inanimate  substances — the  organ 
to  be  affected,  and  the  stimulus.    For  this  opinion  there  is 


17 

direct  evidence ;  we  know  that  the  corporeal  organs  are 
kept  in  motion  during  life,  by  the  direct  action  of  stimuli ; 
and  we  know  further,  that  after  death,  the  action  of  many 
may  be  revived  by  the  same  means.  What  agency,  then, 
can  such  irritable  matter  have  in  the  regeneration  of  itself, 
when  the  strongest  character  which  it  possesses  proves 
liow  very  subject  it  is  to  be  affected  by  the  action  of  in- 
animate substances  ?  This  irritability  is  the  true  life  ;  and 
it  is  in  vain  to  try  to  establish  any  other  principle  be- 
cause the  living  power  seems  more  complex.  We  cannot 
deny  life  to  plants,  and  yet  the  most  fanciful  inquirer  has 
never  been  able  to  allow  them  more  than  an  irritable  pro- 
perty. To  lower  the  vegetable  power  of  life  beyond  this 
point  is  not  requisite,  though  it  has  been  attempted  more 
than  once.  This  power  of  life,  in  plants,  is  even  more 
distinct  than  in  the  polypus  and  other  inferior  animals,  as 
the  following  instances  will  show. 

"  The  stamina  of  the  cistus  helianthemwn  are  seen  to 
move  in  various  directions,  when  the  sun  shines  upon 
them ;  the  leaves  of  the  mimosa  pudica  (sensitive  plant) 
when  touched  by  the  hand,  or  when  irritated  by  the  alight- 
ing of  an  insect  on  them,  immediately  contract;  dionea 
muscipula,  (Venus'  fly  trap,)  when  a  fly  touches  its  leaves, 
closes  the  thorny  fringes  with  which  they  are  beset 
on  the  presumptuous  insect,  and  crushes  it  to  death  ;  but 
the  motions  of  the  hedysarum  gyrans  are  the  most  re- 
markable of  all  those  that  take  place  in  plants.  The 
leaves  of  this  extraordinary  vegetable  are  seen  in  con- 
stant motion  through  the  greater  part  of  the  day,  without 
the  intervention  of  any  apparent  external  impulse ;  and 
even  when  a  branch  is  cut  off,  and  kept  in  water,  the  mo- 
tion of  the  leaves  continues  for  many  hours  together.  All 
the   plants  which  grow  above   the    earth   expose   their 

3 


18 

leaves  and  flowers  to  the  warm  sunshine,  and  when  situa- 
ted in  a  place  which  is  supplied  by  light  only  from  one 
quarter,  they  gradually  direct  their  branches  toward  that 
part  by  which  the  light  enters.  In  stormy  weather,  they 
retract  their  leaves  and  fold  up  their  flowers ;  and  when 
confined  in  the  dark,  their  branches  retain  the  position 
which  they  had  when  exposed  to  the  light."*  We  surely 
cannot  compare  with  such  vegetable  life  that  of  the 
oyster,  which  is  equally  rooted  to  the  mud  or  ground  ;  or 
of  the  polypus,  which  is  washed  about  by  the  troubled 
water  without  manifesting  the  least  exertion  of  will.  In 
these  examples,  we  perceive  that  life  is  nothing  more  than 
irritability  diffused  through  the  corporeal  structure.  In 
the  higher  classes,  as  among  testacise,  quadrupeds,  birds, 
and  mankind,  irritability  is  equally  the  principle  of  life; 
but  the  organization  is  so  much  more  complicated  that 
that  principle  becomes  multiplied.  Thus  we  say  they 
have  sensibility  as  well  as  irritability.  Physiologists  have 
endeavoured  to  impress  the  idea  of  a  great  difference  be- 
tween these  two  characteristics.  They  appear,  however, 
in  the  end  to  be  constituted  by  the  same  principle,  and 
differ  only  in  their  mode  of  application.  Nerves  are  ne- 
cessary for  sensibility,  whereas  irritability  is  possessed  by 
organic  matter,  wherein  nerves  have  never  been  traced. 
So  far  there  is  a  manifest  difference.  But  what  principle 
constitutes  the  power  of  action  in  nerves  ?  It  must  ulti- 
mately be  dependent  upon  irritability,  which,  as  I  have 
remarked,  is  life  in  every  form.  The  following  example 
will  show  their  similarity  of  principle,  as  well  as  an  osten- 
sible difference  in  their  results.  When  a  muscular  part 
meets  with  a  violent  injury,  it,  in  the  first  place,  inflames 
in  consequence  of  the  irritability  residing  in  its  compo- 

*  Encyc.  Brit,  Physiol. 


19 

nent  parts,  which  are  all  injured  ;  but  if  mania  or  sympa- 
thetic inflammation  (as  generally  understood^  supervene 
elsewhere,  it  is  because  the  nerves  and  other  connecting 
organs,  by  the  first  impression,  have  been  irritated,  and 
they  are  endowed  with  the  power  of  transferring  the  ex- 
citement. From  similar  arguments  we  must  be  led  to 
the  conclusion,  that  there  is  but  one  vital  principle,  whe- 
ther with  or  without  nerves ;  that  such  irritability  is  pecu- 
liar to  every  part  of  the  living  matter,  independent  of  the 
system  at  large ;  and  that  the  nervous  extension  is  for  the 
purpose  of  concentrating  this  diffused  animation,  as  well 
as  for  transferring  internal  and  external  stimuli  to  each 
part,  without  which,  though  thoroughly  organized,  they 
would  be  inanimate:  furthermore,  all  this  co-operating 
structure  is  constantly  wasting  away,  though  endowed 
with  vitality ;  hence  another  system  of  organization  be- 
comes necessary,  which,  while  diffused  through  all  parts, 
makes  up  the  full  power  of  life,  not  by  connecting  those 
parts  together,  but  by  bringing  to  each  a  supply  of  blood, 
which  preserves  the  irritable  composition.  Having  thus 
examined  the  true  form  of  life,  and  found  it  to  be  irrita- 
bility, let  us  now  view  this  property  more  particularly, 
that  thus  we  may  estimate  the  vital  power  in  the  formation 
of  animated  matter. 

Baron  Haller  was  of  opinion,  that  irritability  existed 
independent  of  a  nervous  connection,  and  therefore  called 
it  a  vis  insita  of  the  part  itself.  We  have  seen  in  vegeta- 
bles, that  nerves  are  not  necessary  for  life  ;  the  polypus 
seems  an  instance  among  animals.  The  umbilical  cord 
has  never  shown  the  least  trace  of  a  nervous  texture  ;  and 
accordingly,  when  divided,  occasions  no  sensation  of  pain 
to  the  female,  and  apparently  none  to  the  foetus  :  yet  we 
cannot  but  allow  it  has  life.     If  nerves  were  necessary  for 


20 

vitality  in  this  part,  it  is  highly  probable,  that  they  would  at 
least  be  as  manifest  as  those  of  the  foetus,  which  are  neces- 
sarily supplied  with  nutriment  after  the  cord.  The  fibrine 
of  the  blood,  which  we  can  scarcely  suppose  to  be  affected 
by  the  nervous  power  when  taken  out  of  the  body,  is  still 
susceptible  of  irritation.  This  curious  fact  was  first  stated 
by  Circaud,  and  afterwards  confirmed  by  Delametherie.* 
The  difficulty  of  succeeding  in  such  experiments  must 
evidently  be  very  great ;  for  when  we  consider  how  very 
soon  irritability  is  destroyed  by  the  least  change  of  com- 
position, we  cannot  be  surprised  at  failing  to  illustrate  the 
power  in  fibrine.  But  it  is  of  little  consequence  to  prove 
the  absence  of  nerves  ;  since  in  these  also  irritability  may 
be  considered  as  a  vis  insita.  The  term  itself  is  far  more 
questionable ;  for  irritability  is  not,  strictly  speaking,  any 
thing  else  than  a  property  of  matter.  Common  language, 
it  is  true,  gives  sanction  to  such  an  application  ;  but  it  is 
evidently  incorrect  to  style  that  a  power  which  absolutely 
depends  for  its  existence  upon  something  else.  In  this 
case  particularly,  it  becomes  necessary  to  preserve  this 
view,  in  as  much  as  it  points  to  the  common  error,  of 
thinking  life  a  cause,  instead  of  an  effect.  There  is  no 
such  thing  known  as  irritability,  without  the  influence  of 
a  stimulus,  and  when  this  property  is  made  manifest,  we  can 
only  consider  it  as  a  secondary  existence.  We  say  a 
body  is  sweet  or  sour,  but  we  know  that  such  qualities 
are  dependent  upon  the  gustatory  nerves,  as  much  as 
on  the  body  itself.  So  it  is  precisely  with  life,  which  is  a 
quality  generated  by  stimulus  upon  the  organic  matter. 
This  truth,  when  we  conjoin  the  mode  of  action  by  stimu- 
li, must  lead  us  to  consider  irritability  as  much  a  material 
property  as  those  which  we  daily  call  so.      It  depends 

*  Bostock's  History  of  Galvanism. 


21 

upon  the  chemical  composition  more  than  shape  or  mag- 
nitude ;  and  is  therefore  very  analogous  to  a  chemical 
property.  Such  a  conclusion  may  seem  too  hasty,  and 
perhaps  is,  since  experiments  to  the  point  are  very 
few  in  number.  Elsewhere  I  shall  endeavour  to  do  more 
justice  to  this  subject,  when  treating  of  irritability,  as  re- 
sulting immediately  from  the  composition  of  organic  mat- 
ter, and  as  being  in  truth  a  part  of  the  assimilating  pro- 
cess. Persons  who  are  unwilling  to  suppose  life  any  thing 
else  than  a  perfect  archeus,  making  the  body  his  home 
until  death  turns  him  out,  have  supposed  that  wherever 
this  principle  has  been  revived,  it  must  have  existed 
throughout,  only  in  a  latent  state.  The  moment,  however, 
this  opinion  is  examined,  its  truth  becomes  questionable, 
at  least,  as  to  the  application  in  many  cases.  Irritability, 
we  know,  can  be  manifest  only  as  long  as  a  stimulus  is 
present.  How  then  can  we  suppose  a  vital  action,  or 
even  a  latent  vital  power,  when  no  stimulus  is  concerned  ? 
Wharever  may  be  the  appearance,  we  may  conclude,  that 
whenever  life  appears,  the  organization  must  have  remain- 
ed unimpaired  ;  consequently,  in  all  such  cases,  life  may 
really  be  destroyed  and  restored.  If  an  egg,  for  instance, 
can  after  any  lapse  of  time  produce  a  chicken,  the  foetal 
structure  must  through  that  lapse  have  remained  unalter- 
ed as  to  its  chemical  composition,  as  well  as  arrangement. 
Hence,  then,  the  appearance  of  life  in  this  case  may  be  re- 
conciled with  observation  upon  the  living  body  itself  -r  in 
which  we  know  the  vital  power  has  no  existence,  without 
a  proper  stimulus,  and  where  we  see  that  its  regeneration 
depends  upon  that  stimulus.  The  heart,  for  instance,  con- 
tracts violently,  as  long  as  the  lungs  inhale  the  atmospheric 
oxygen,  but  when  hydrogen  is  breathed,  or  any  other  gas 
which  cannot  readily  unite  to  the  carbon  of  the  blood,  the 


22 

heart  languishes,  and  approaches  true  death.  For  the  same 
reason  we  see  why  a  seed  appears  to  be  dead  (and  really 
is  so  when  without  a  stimulus)  for  many  years  ;  but  when 
exposed  to  the  influence  of  heat,  air,  moisture,  &c.  acquires 
life.  The  structure  is  capable  of  being  excited  at  any 
time  before  decomposition  takes  place.  In  Smith's  work  on 
Botany,  we  find  an  instance  where  a  plant,  after  being 
kept  twelve  or  fourteeen  months,  as  a  dry  specimen,  ob- 
tained life  upon  being  planted.  Now,  in  this  case  all  kind 
of  nutriment  had  been  withheld  ;  and  not  only  this,  but  the 
stimuli,  which  at  other  times  are  found  to  be  absolutely 
necessary  for  life.  Here  then  I  think  the  subsequent 
growth  plainly  shows  that  the  oganization  (which  in  plants 
is  always  more  permanent  than  in  animals)  remained  so 
little  impaired,  that  the  natural  stimuli  of  warmth,  air, 
and  moisture,  were  enabled  to  excite  its  actions,  or,  in  other 
words,  to  create  life.  Whenever  the  structure  is  simple, 
irritability  will  remain  longest ;  for  decomposition  is  then 
slowest  in  its  effects.  For  this  reason,  it  is  so  difficult  to 
preserve  the  life  in  animal  substances,  after  they  have  been 
exposed  to  injury,  which  almost  always  is  followed  by  a 
decomposition.  An  egg  is  rendered  unfit  for  hatching  by 
a  few  shakes  ;  whereas  the  same  will  not  affect  a  seed. 

By  keeping  in  view  that  irritability  is  a  property  of  mat- 
ter, and  not  a  separate  power,  we  will  be  enabled  to  value 
its  influence  over  the  formation  of  animated  matter.  As 
such,  it  must  be  confined  to  the  substance  possessing  it,  and 
in  no  case  can  effect  a  change  of  composition  in  adjoining 
matter.  We  might  as  well  suppose  that  the  sweetness  of 
sugar  could  convert  things  of  an  opposite  nature  into 
sugar  by  mere  contact.  Before  our  food  becomes  assi- 
milated, it  must  be  totally  changed  in  composition  and 
properties ;  it  generally  also  passes  from  the  solid  to  the 


25 

fluid  state.  Now,  it  is  an  unsupported  supposition  that 
vitality  can  affect  cohesion,  or  a  change  of  chemical  con- 
stitution, and  it  becomes  apparently  impossible,  when  we 
consider  that  this  vital  power  must,  under  such  circum- 
stances, be  supposed  to  exist  in  tubes  and  cavities,  where 
there  is  no  animated  matter.  No  part  of  the  living  econo- 
my has  been  more  mistaken  than  that  of  regeneration. 
In  spite  of  daily  observation,  that  chemical  phenomena 
take  place  in  some  of  the  vital  functions,  and  the  still 
more  imperious  truth,  that  no  process  in  nature  is  known  to 
be  capable  of  altering  the  composition  of  matter,  except 
that  resulting  from  chemical  affinity,  yet  every  subterfuge 
is  grasped  at  to  limit  this  universal  law.  We  can  behold 
the  arm  move  with  mechanical  advantages  ;  the  eye  regu- 
lated by  the  laws  of  optics,  and  the  ear  by  those  of  ac- 
coustics,  and  yet  though  the  laws  of  chemistry  equally 
bespeak  wisdom  and  design,  we  take  upon  ourselves  to 
disturb  a  harmony  which  pervades  the  whole  created 
world.  It  is  doing  no  less  if  we  deny  the  power  of  chemi- 
cal affinity  in  the  composition  of  matter,  merely  because 
it  is,  or  is  to  be  animated,  and  that  too  while  we  confess  a 
total  ignorance  of  the  vital  power.  The  undeniable  truth 
is,  that  the  living  system  is  made  and  supported  by  physi- 
cal laws,  and  that  the  only  power  of  life  consists  in  making 
them  co-operate.  All  the  changes  which  take  place  in 
the  body  must  be  affected  by  these  laws ;  even  to 
the  acquisition  of  vitality.  They  are  all  absolutely 
necessary,  and  those  of  chemistry  the  most  extensive. 
Let  our  prejudices  be  what  they  may,  we  should  be  open 
to  conviction.  If  we  cannot  conceive  the  mode,  we  should 
rather  set  it  down  to  ignorance,  which  will  long  be  the  case 
as  to  our  extent  of  chemical  knowledge.  Besides,  it  should 
be  borne  in  mind  that  the  misdoubt  is,  after  all,  about  a 


24 

trifle.  The  application  of  physical  principles  to  the  phe- 
nomena of  life,  cannot  make  the  nature  of  either  more  in- 
significant to  the  eye  of  philosophy.  On  the  contrary,  it 
completes  that  chain  which  binds  the  universe,  and  con- 
nects the  gradations  of  its  substances,  from  the  simple  atom 
to  the  most  complicated  form  of  organization  and  life. 
Can  the  wisdom  of  God's  works  be  less  divine  because 
they  exhibit  connexion  and  uniformity ;  or  does  the  wis- 
dom displayed  in  them  appear  more  limited  because  it  be- 
comes more  manifest  ?  Certainly  not.  And  the  individual 
who  shuns  or  neglects  the  examination  of  His  works,  is  far 
more  likely,  from  ignorance,  to  err.  than  he  who  aspires  to 
trace  their  symmetry  and  connexion.  Whatever  may  be 
our  doctrines,  it  never  can  derogate  from  the  divine  stamp 
of  life,  to  prove  that  it  derives  advantages,  or  even  exist- 
ence, from  regulations  which  we  all  must  feel  were  framed 
by  the  same  wisdom. 

But  now  it  may  be  asked,  if  there  is  no  power  of  life  in 
the  organized  compound  to  protect  it  from  the  laws  of  che- 
mistry, how  does  it  happen  that  the  structure  is  able  to 
resist  decomposition  ?  This  I  shall  attempt  to  illustrate 
upon  principles  which,  in  my  opinion,  lead  to  the  true 
vital  economy;  since  they  show  that  chemical  changes 
can  take  place  at  all  times  upon  a  living  solid,  but  that 
our  functions  are  regulated  so  that  the  circumstances  un- 
der which  they  occur  shall  not  be  long  injurious.  Phy- 
siologists who  deny  the  power  of  this  action,  evidently 
draw  their  conclusions  from  the  life  of  the  body  at  large. 
Let  them  take  the  whole  to  pieces,  and  then  value  the  in- 
herent power  of  life.  If  the  corporeal  structure  does  not 
perish  by  every  local  decomposition  or  injury,  it  is  be- 
cause that  derangement  is  adjusted  before  it  extends  to  the 
most  important  organs.     This  surely  is  not  to  be  con- 


25 

sidered  in  the  light  of  a  contra-chemical  power  !  The  in- 
jury really  takes  place,  and  the  wisdom  of  our  conforma- 
tion consists  in  making  amends  for  the  action  of  laws 
which  cannot  be  subdued  as  long  as  matter  exists.  Take 
the  mortifying  leg  of  an  animal ;  do  we  not  there  see  the 
true  life  diminishing  ?  It  is  a  portion  of  the  general  stock, 
which  evidently  is  insufficient  in  its  nature  to  prevent  che- 
mical decomposition.  Here,  also,  we  may  value  the  power 
ofhfe,  which  consists  in  the  arrangement  of  parts,  and  not 
in  giving  them  magic.  As  long  as  the  blood  vessels,  nerves, 
and  other  connecting  organs  remain  undecomposed,  they 
will  possess  perfect  irritability,  and  so  long  will  be  enabled, 
by  the  increased  stimulus,  to  bring  a  share  of  blood  to  the 
mortifying  limb,  sufficient  to  re-compose  its  parts.  The 
absorbents  at  the  same  time,  and  by  the  same  means,  take 
up  and  separate  the  detached  portions ;  thus  preventing 
their  further  reaction  on  the  limb.  But  if  all  this  beauti- 
ful connexion  looses  the  capacity  for  life  or  irritability,  in 
consequence  of  being  involved  in  the  decomposition,  no 
power  or  spirit  can  support  the  limb.  Chemical  changes 
progress  as  they  did  from  the  beginning,  but  the  structure 
which  they  destroy  is  not  rebuilt,  and  the  whole  sloughs 
away.  It  may  indeed  be  removed  by  fluids  secreted  from 
the  living  extremities,  as  well  as  by  those  which  result 
from  the  decomposition.  These  terminations  generally 
prove  successful  in  preserving  the  life  of  a  portion,  and 
indicate  the  most  perfect  design. 

Very  few  will  have  it  in  their  power  to  disprove  the 
true  character  of  the  chemical  changes  which  take  place 
in  the  forgoing  example;  but  it  may  happen  that  the  liv- 
ing texture  shall  meet  with  a  similar  exposure,  and  yet  no 
fatal  results  follow.  Whatever  may  be  the  appearance,  we 
are  justified  in  applying  to  all  such  instances  the  foregoing 

4 


26 

principles  ;  since  the  organic   arrangement  being  still  the 
same,  the  mode  can  only  differ  in  extent. 

The  parts  exposed,  even  if  they  should  suffer  incipient 
decomposition,  are  immediately  roused  where  life  (or  as 
we  consider  it,  irritability)  yet  remains,  in  proportion  to 
the  complexity  of  structure  •  fluids  are  thrown  out  on  the  li- 
ving surface,  which  they  shield  from  decomposition,  by  re- 
moving the  chemical  agent  beyond  the  sphere  of  its  action. 
Here  we  see  no  proof  that  the  life  of  the  parts  exposed 
resisted  the  chemical  tendencies.  That  which  follows 
being  a  proof  that  the  animated  matter  has  not  the  slight- 
est power  of  defending  itself,  but  that  it  melts  with  all 
its  success  in  consequence  of  connexion  and  arrangement. 

If  the  chemical  agent  be  small  and  light,  it  becomes 
washed  away,  in  a  similar  manner  to  what  takes  place 
when  a  grain  of  sand  or  dust  enters  the  eye.  This  may 
be  done  before  even  the  fluid  which  is  employed,  can  suffer 
decomposition  from  the  same  substance.  But  when  this 
agent  is  lodged  to  any  depth,  or  is  too  heavy  to  be  washed 
away,  a  chemical  action  always  takes  place  independent 
of  mechanical  irritation.  If  a  small  quantity  of  white  arse- 
nic (arsenious  acid)  be  swallowed,  it  enters  one  of  the 
most  vital  organs  of  the  body;  yet  it  may  pass  through 
the  whole  course  of  the  stomach  and  intestines,  without 
producing  more  than  a  trifling  inflammation,  wherever  it 
meets  with  detention.  The  reason  is  obvious,  and  shows 
how  very  feeble  any  specific  life  (or  that  which  belongs  to 
a  single  part,)  must  be.  We  find  that  a  fluid  is  always 
necessary  to  bear  away  the  foreign  material,  and  from 
this  we  conclude,  that  the  provision  has  been  made,  not 
to  destroy  the  tendency  towards  action,  but  by  interposi- 
tion, to  remove  the  materials  from  each  other,  and  they 
prevent  a  result  which  otherwise  would  as  soon  take  place 
in  the  body  as  out  of  it.    Such  an  arrangement,  instead  of 


27 

diminishing  the  wisdom  of  our  construction,  infinitely  ex- 
alts it.  It  shows  a  consistency  with  the  rest  of  matter, 
without  having  to  suppose  that  the  life  changes  properties 
which  are  immutable  elsewhere. 

Persons  who  deny  the  power  of  chemistry  over  anima- 
ted matter,  contend  that  the  absence  of  gaseous  matter  is 
a  proof.  But  here  again,  the  system  at  large  is  considered 
instead  of  any  single  part ;  we  all  know  that  when  chemi- 
cal action  takes  place  to  any  extent  in  a  limb,  in  the  intes- 
tines, or,  in  short,  in  any  other  portion,  that  gases  are 
abundantly  formed.  But  the  objection,  when  even  appli- 
cable to  the  whole  system  is  unsupported.  What  else  can 
we  consider  respiration  but  a  chemical  function  ?  It  is  idle 
to  object  to  this  example,  because  respiration  is  not  per- 
formed within  the  substance  of  the  body  5  but  merely  on 
the  pulmonary  surfaces.  Are  we  to  dispute  about  trifles, 
when  the  principle  is  unimpeached  ?  Surely,  if  respiration 
be  necessary  to  life,  so  must  the  chemical  changes;  which 
may  therefore,  as  to  principle,  take  place  as  well  in 
the  body  as  out  of  it.  If  we  expect  gases  to  be  liberated 
in  any  quantity  during  the  exercise  of  the  functions,  we 
are  evidently  going  too  far ;  since,  after  all,  chemical 
changes  of  the  most  varied  nature  may  take  place  with- 
out the  production  of  any  gas.  We  know  that  all  corpo- 
real changes  during  life  are  in  appearance  very  gradual ; 
and  therefore,  although  gases  should  be  formed,  they  must 
pass  away  unobservable  in  magnitude,  by  the  circulating 
blood.  As  long  as  the  decomposition  subtracts  only  one 
ingredient  at  a  time,  as  carbon,  and  as  long  as  health  re- 
mains to  re-establish  the  original  compound,  by  speedily 
furnishing  new,  but  similar  matter,  so  long  it  must  follow, 
that  little  or  no  gas  will  be  manifest.  The  chemical 
changes  of  the  living  body  need  not,  of  necessity,  be  the 
same  as  those  which  take  place  in  the  cadaverous  mass, 


28 

where  all  the  constituents  are  liberated  nearly  at  the  same 
time,  and  where  it  would  indeed  be  singular  if  gaseous 
products  were  not  formed.  But  after  all,  if  nothing  can 
satisfy  such  doubters  but  facts,  I  need  only  refer  to  Pro- 
fesssor  Brande's  experiments,  as  related  by  Sir  Everard 
Home,  where  two  cubic  inches  of  carbonic  acid  gas  were 
obtained  from  every  ounce  of  fresh-drawn  blood.  This, 
it  may  be  remarked,  is  the  gas  which  always  results  from 
organic  decomposition,  and  agrees,  in  quantity,  with  the 
gradual  changes  of  the  living  body. 

Another  objection  has  been  advanced,  which  at  first 
sight  appears  forcible.  One  of  the  great  phenomena  of 
chemical  affinities  is,  that  the  more  complex  a  substance  is 
in  composition,  the  sooner  it  yields  to  spontaneous  changes. 
Thus,  when  a  body  has  two  constituents,  it  is  more  firmly 
constituted  than  when  one  of  these  becomes  multiplied,  or 
where  a  third  ingredient  exists.  During  life,  however, 
such  parts  which  are  always  the  most  vital  seem  the  least 
prone  to  decomposition  ;  and  it  is  said  that  life  must  be 
the  cause,  since  when  such  parts  are  dead,  they  readily 
obey  the  common  law.  I  have  already  said,  that  the 
laws  of  matter  have  all  their  force  in  the  living  body  as 
well  as  in  the  universe.  This,  1  feel  persuaded,  is  infi- 
nitely more  consistent  than  to  suppose  that  matter  can 
exist  any  where  without  them.  The  present  subject  fur- 
nishes a  demonstration  which,  to  me,  appears  capable  of 
upholding  such  an  opinion. 

It  is  impossible,  by  any  process  of  reasoning,  to  devest 
ourselves  of  the  conviction,  that  the  living  substance  has 
most  of  its  properties  in  common  with  the  dead.  In  com- 
position it  certainly  is  similar,  (as,  for  instance,  the  dead 
and  living  muscle,)  consequently,  although  the  decomposi- 
tion may  be  more  manifest  in  one  than  in  the  other,  we 


29 

must  suppose  its  principles  alike  for  both.  This  general, 
though  correct  consideration,  leads  us  to  expect  the  fore- 
going law  of  composition  should  hold  true  in  vital  and 
highly  organized  parts  of  the  body;  accordingly  the  ap- 
pearance which  such  parts  have  of  resisting  chemical  changes 
admits  of  an  explanation  agreeable  both  to  the  phenomena 
of  life,  and  the  general  law  of  matter. 

All  parts  of  the  body  which  are  most  complex  are  also 
most  vital ;  or,  in  other  words,  they  are  most  largely  sup- 
plied with  blood-vessels,  nerves,  and  other  connecting 
organs.  These  are  considered,  in  vague  language,  merely 
as  characteristics  of  life ;  but  I  conceive  the  design  of  our 
conformation  can  be  traced  much  farther.  They  appear 
as  constituting  an  arrangment,  not  to  subvert  chemical  af- 
finities, (without  which  no  organized  substance  can  exist,) 
but  to  make  amends  for  their  undeviating  sway.  To  the 
complex  structure  we  may  apply  the  general  law,  and  by 
the  living  properties,  which  seem  in  opposition,  prove  its 
truth.  We  may  say  that  the  complex  vital  structure  un- 
dergoes decomposition  quicker  or  more  readily  than  the 
simple  one  ;  and  for  this  reason  it  is  furnished  with  a  much 
greater  supply  of  blood,  that  thus  it  maybe  rebuilt  without 
the  whole  system  being  injured.  Other  parts,  as  the 
nails  and  hair,  are  of  uniform  composition,  and  are  well 
known  to  resist  chemical  decomposition  •  they,  therefore, 
need  not  be  furnished  with  blood  throughout,  and  are  in- 
animate when  compared  with  the  foregoing.  This  de- 
struction, previous  to  absorption,  is  not  a  mere  conjecture  ; 
the  cohesion  which  could  take  place  at  the  mouths  of  the 
absorbents  must  evidently  be  too  powerful,  subsequently, 
for  those  mouths  to  eat  down,  as  Mr.  Hunter  supposed, 
or  to  be  nibbled  as  by  the  mouth  of  a  worm.  "  A  mere 
conjecture,  and  most  improbable.     The  solids  are  raised 


30 

by  the  agency  of  the  vessels  on  the  chemical  affinities  of 
the  circulating  fluids.  They  must  be  resolved  by  a  pro- 
cess reducing  them  again  to  the  state  of,  fluids,  or  the  se- 
creting vessels  throw  out  fluids  which  dissolve  them ;  an 
operation  anterior  to  their  absorption."*  The  brain  is  an 
instance  of  a  very  vital  part,  so  is  the  womb  ;  accordingly 
we  find,  as  John  Bell  remarks,  that  they  "  are  the  most 
liberally  supplied  with  blood."  Again,  as  the  brain  is  the 
least  firm  of  the  two,  we  should  conclude  that  it  must, 
also,  be  most  liable  to  decomposition  ;  and,  as  if  to  make 
amends  for  this  state,  we  find  that  it  has  "  two  great  arte- 
ries on  each  side ;  it  has  two  carotid,  and  two  vertebral 
arteries  ;  they  far  surpass  those  of  the  womb  ;  their  inos- 
culations are  so  particular  that  there  are  no  others  like 
them  in  all  the  body.  The  injection  of  any  one  artery 
easily  fills  the  whole ;  the  preservation  of  but  one  artery 
saves  the  life  of  the  creature  when  the  others  are  stop- 
ped." What  can  be  more  reasonable  than  to  suppose  that 
this  singular  inosculation  is  for  the  purpose  of  supplying, 
under  the  worst  of  circumstances,  a  ready  stock  of  blood 
to  obviate  the  fatal  effects  of  rapid  decomposition  ?  "  The 
brain,  which  weighs  not  a  fortieth  part  of  the  whole  body, 
receives  one  tenth  of  all  the  blood :  a  proportion  which 
must  occasion  surprise."  Every  person  who  has  made 
repeated  dissections  of  this  organ  must  have  observed^how 
very  soon  it  becomes  destroyed  after  death  has  taken 
place  •,  and  the  same  tendency  cannot  but  exist  during 
life.  The  spinal  marrow  is  also  well  supplied  with  blood 
from  the  anterior  spinal  artery,  which  descends  along  the 
medullary  column  in  a  furrow  formed  for  itself,  and  sends 
innumerable  branches  into  its  substance. 

*  J.  Bell's  Anat 


31 

Thus  are  obviated  some  of  the  principle  objections 
against  the  anti-chemical  power  of  life  peculiar  to  the 
solids.  If  there  be  any  truth  in  the  position,  how  shall 
we  deny  the  tendency  to  chemical  changes  among  our 
"various  kinds  of  food  and  the  fluids  generally,  which  are 
within  cavities,  and  appear  to  have  no  permanent  con- 
nexion with  the  solid  structure  ?  If  changes  in  them  are 
not  fatal  to  the  whole  system,  it  is  because  they  are  kept 
in  progressive  motion  through  these  cavities  and  canals, 
until  they  receive  suitable  changes  of  composition,  from 
chemical  agents  placed  in  their  way,  being  then  separated 
from  the  mass  by  absorption,  or  expelled  from  the  body 
before  injurious  accidents  can  take  place.  Another  rea- 
son why  the  body  escapes  chemical  injuries  during  its  pro- 
gress is,  that  the  substances  which  enter  by  the  mouth, 
are  in  general  mild  nutritives,  which  readily  submit  to  the 
changes  of  assimilation.  When  by  accident  or  design, 
chemical  agents  of  a  more  powerful  nature  are  made  use 
of,  we  see  too  clearly  that  life  is  either  prostrated  or  ex- 
tinguished. 

As  to  fluids,  a  few  remarks  will  show  why  they  in  par- 
ticular undergo  ready  changes  of  composition.  Let  us 
take  the  blood  as  an  example,  since  this  gives  evidence 
of  possessing  irritability.  This  fluid  is  of  a  compound 
nature,  not  only  by  its  own  constitution,  but  by  the 
continual  intermixture  of  foreign  materials.  Its  con- 
tact with  the  vital  texture,  is  incessantly  changing  ;  it  has 
no  diffused  organs  through  its  substance,  for  the  purpose 
of  repairing  chemical  changes,  and  without  the  slightest 
arrangement  to  concentrate  its  vital  property.  What  then 
has  it  to  make  amends,  but  this  simple  quality  of  irritabi- 
lity ?  We  have  already  seen  how  poor  a  protection  this 
is  to  the  solid  texture  ;  how  much  less,  then,  must  it 
be  to  the  blood,  which,  as  a  fluid,  has  not  even  a  percepti- 


32 

ble  affinity  of  aggregation,  to  oppose  decomposition  ;  its 
fluidity  not  only  assists  its  own  destruction,  but  gives  the 
same  power  to  the  intermixed  matter.  We  accordingly 
iind  that  the  blood  does  meet  with  such  changes  to  a  cer- 
tain extent.  They  are  always  made  more  manifest 
in  diseases  with  languid  circulation;  and  would  un- 
doubtedly have  a  fatal  issue,  were  it  not  that  a  pro- 
vision is  made  to  separate  these  foreign  substances, 
and  to  purify  the  blood  itself,  at  the  end  ot  every  round. 
Circulation  has  this  for  one  of  its  important  objects.  Each 
part  of  this  fluid  undergoes  a  complete  review,  as  it  were, 
in  the  lungs  ;  and  before  the  course  of  circulation  becomes 
complete,  a  great  part  of  the  blood  itself,  as  well  as  its 
admixtures,  are  timely  disposed  of,  in  the  form  of  secretion 
and  excretion.  Similar  exposure  and  provision  may  be 
observed  for  all  the  other  fluids.  In  this  way,  injury  is 
prevented ;  not  by  destroying  chemical  action,  but  by 
withdrawing  the  materials  from  each  other,  which  other- 
wise would  display  their  affinities,  nowithstanding  the  sup- 
posed check  of  an  inherent  vital  principle. 

CHEMICAL    AGENTS    IN    THE    FORMATION    OF    ANIMATED 
MATTER,    AND    ITS    FUNCTIONS. 

We  have  already  anticipated  a  great  deal  of  the  part 
which  chemistry  performs  in  the  vital  functions.  The 
more  these  are  examined  the  more  one  must  be  convinced, 
that  the  proximate  cause  of  all  organic  formation  is  che- 
mical affinity.  It  is  not  reasonable  to  expect  a  detail  of 
operations,  so  varied  and  unobservable  in  their  nature ; 
neither  is  it  neccessary.  But  we  have  general  rules  which 
are  sufficient  to  establish  the  truth,  without  requiring  that 
every  ambiguous  point  should  be  cleared  up  by  experi- 
ments. The  laws  of  chemistry,  are  the  only  ones  capable 
of  effecting  a  change   of  composition :  its  agents  are  not 


33 

only  surrounding  the  living  structure  5  but  they  pervade 
its  most  important  organs,  and  must  of  necessity  charac- 
terize every  material  production  within  the  system.  Irri- 
tability which  is  the  true  type  of  life  in  the  parts  them- 
selves, cannot  prevent  decomposition,  as  has  been  shown, 
but,  on  the  contrary,  must  always  be  the  proof  of  action, 
no  matter  how  indefinite.  The  phenomena  of  life  when 
connected  from  part  to  part,  cannot  be  regarded  as  show- 
ing that  chemical  affinities  are  subdued,  since  they  admit 
of  an  explanation  perfectly  agreeable  to  both.  When  ex- 
amined, the  true  vital  economy  is  found  not  to  consist  in 
destroying  such  laws,  but  interposing  materials  which 
have  the  power  of  acting  chemically,  and  these,  by  the 
uniformity  of  their  nature  are  generally  attended  with  the 
designed  end.  Hence,  then,  we  can  safely  say  that,  whate- 
ver be  the  form  of  structure  employed,  the  changes  of 
composition  which  take  place  during  life  are  of  a  true 
chemical  nature,  as  well  as  the  agents  employed.  Our 
want  of  power  to  imitate  or  illustrate  these,  argues  only 
our  ignorance  of  the  science.  Every  practical  chemist 
knows  how  much  difficulty  he  has  in  managing  the  few 
articles  which  may  be  placed  in  a  crucible  or  retort ;  and 
every  new  compound  which  he  encounter  requires  the 
same  kind  of  labour  before  he  can  presume  to  announce 
its  nature.  It  would  be  the  height  of  presumption  to  take 
up  a  few  simple  minerals,  and  say  these  constitute  the 
living  fabric  ;  but  it  never  can  be,  to  suppose  that  chemi- 
cal affinity  is  employed  as  much  for  one  as  the  other. 
Neither  is  it  to  be  supposed  that  analysis  will  enable  us 
to  succeed  in  the  composition.  It  is  easy  to  consume  the 
brilliant  by  a  burning  glass  and  to  prove  that  it  consists  of 
carbon ;  but  this  success  gives  no  power  to  form  it  anew. 
Though  possessed  of  the  materials,  and  perfectly  convin- 

5 


34 

ced,  that  they  still  have  the  same  chemical  tendency  as  at 
other  times,  the  only  constant  result  is,  to  be  convinced 
that  it  is  much  easier  to  destroy  than  constitute,  notwith- 
standing the  similarity  of  principle  for  both  processes. 

When  we  confine  our  attention  to  the  higher  range  of  ani- 
mals we  are  inclined  to  consider  that  life  effects  all  their 
phenomena,  and  so  it  does  remotely ;  since  it  is  the  result 
of  organic  arrangement,  and  operates  by  presenting  mate- 
rials. So  does  the  chemist,  when  he  pours  sulphuric  acid 
from  one  glass  into  another  of  carbonate  of  soda,  remote- 
ly produce  the  sulphate.  But  we  must  not  confound  the 
operation  of  his  hands  with  the  affinity  which  constituted 
the  salt,  or  occasioned  the  effervescence.  The  life  of  a 
plant  is  considered  as  a  very  humble  one ;  and  if  such,  so 
must  be  its  power.  Yet  the  secretions  formed  under  such 
circumstances  have  as  much  constitutional  difference  as 
those  of  the  most  perfect  animals,  Here,  then,  there  is 
infinitely  less  opportunity  to  intoduce  this  mysterious  in- 
fluence ;  and  turn  where  we  may,  the  same  outline  is  ob- 
servable. With  this  we  should  be  satisfied,  without  trying 
to  oppose  laws  which  we  can  not  alter. 

MOISTURE    AND    FLUIDITY. 

This  state  of  cohesion  is  observable  all  through  the 
living  stucture,  and  is  so  important  in  promoting  chemi- 
cal action,  as  to  give  rise  to  the  rule  "  corpora  non  agunt 
nisi  sint  soluta."  I  am  not  to  be  understood  as  implying 
that  such  is  their  most  important  use  in  the  body  ;  on  the 
contrary,  when  intermixed,  or  in  contact  with  solids,  they 
are  of  the  most  obvious  use  in  facilitating  motion,  defend- 
ing surfaces  from  chemical  action  by  interposition,  in  pre- 
venting, as  well  as  sometimes  in  effecting  adhesions.     It  is 


35 

t 

equally  true,  however,  that  where  they  effect  a  solution 
they  give  a  greater  opportunity  for  chemical  changes  ;  and 
this  result  is  always  independent  of  the  fluid.  Further- 
more, we  may  say,  that  all  the  important  combinations  are 
effected  by  the  agency  of  solution.  Even  supposing,  with 
Mr.  Hunter,  that  the  "  modelling  absorbents"  eat  down 
the  solid  parts,  still  their  solution  must  be  effected  before, 
or  shortly  after  their  being  swallowed.  Such  is  the  state 
at  least  when  they  are  examined  in  the  thoracic  duct,  and 
such  must  be  their  state  before  they  can  circulate  with 
the  blood.  Every  part  of  the  solid  texture  has  a  moist  or 
liquid  matter  pervading  it ;  hence  it  is  but  reasonable  to 
suppose  that  this  is  a  means  employed  to  render  the  differ- 
ent parts  fit  for  being  absorbed,  as  soon  as  their  texture 
looses  its  aggregation.  As  the  fluids  are  not  united  to  the 
system  at  large  by  interwoven  nerves  or  blood  vessels,  we 
cannot  suppose  them  capable  of  resisting  chemical  changes, 
or  of  making  amends  for  themselves,  after  such  have  taken 
place.  With  them,  as  with  every  other  part  of  the  body, 
extensive  and  uninterrupted  connexion  is  necessary. 
Fluids,  therefore,  are  absorbed,  and  thus  brought  into  new 
ranges  of  affinities,  suitable  to  the  general  economy,  or 
are  by  the  same  act  checked  in  their  tendency,  by  divid- 
ing the  mass  before  it  can  take  place.  Another  arrange- 
ment, also,  effects  the  same  end.  The  slowest  motion 
among  the  particles  of  a  fluid,  unless  they  possess  a  very 
powerful  affinity  for  each  other,  tends  to  prevent  their  re- 
maining in  contact  long  enough  to  combine.  This  is  also 
aided  by  the  water  which  constitutes  so  large  a  portion 
of  their  bulk ;  as  a  solvent  it  separates  the  particles  be- 
yond the  sphere  of  action.  But  with  all  these  provisions, 
there  can  be  no  doubt  but  that  the  fluids  are  proximately 
the  field  wherein  all  the  organic  formations  and  destruc- 


36 

tions  take  place.  In  their  arrangement  we  behold  a  con- 
stant view  towards  their  chemicai  and  physical  quality. 
The  mucous  fluids  are  generally  secreted  upon  surfaces 
which  have  outlets  through  the  body ;  because,  as  they 
have  the  property  of  coagulating  under  circumstances, 
they  would  often  prove  injurious  by  occasioning  improper 
adhesions,  unless  there  were  means  of  expelling  them. 
The  serous  fluids,  since  they  have  not  the  chemical  pro- 
perty of  the  other  are  deposited  upon  the  surfaces  of  en- 
closed cavities,  as  within  the  peritoneum,  pleura,  or  the 
capsules  of  joints.  There  are  other  fluids  secreted  for 
the  express  purpose  of  chemical  action;  such  are  the  gas- 
tric and  pancreatic  juices,  the  bile,  saliva,  and  various 
others,  but  it  is  not  necessary  to  consider  them  in  this 
place  more  minutely,  since  their  chemical  agency  de- 
pends upon  their  composition  rather  than  their  state  of 
cohesion. 

ANIMAL    HEAT. 

This  is  also  an  auxiliary.  We  find  it  nearly  equally  dif- 
fused throughout  the  body  ;  and  its  presence  is  sufficient  to 
promote  chemical  changes,  without  inquiring  into  its  origin. 
It  is  the  degree  of  temperature  which  seems  most  active 
in  giving  bodies  their  solid,  fluid,  and  gaseous  forms.  As 
such,  it  must  be  regarded  as  similar,  in  its  agency,  to  the 
foregoing ;  that  is,  in  influencing  the  aggregation  upon 
which  chemical  action  in  a  great  measure  depends.  It 
must  be  confessed,  however,  that  it  seems  more  useful  in 
keeping  up  a  constant  excitement  in  the  irritable  texture. 
We  feel  how  completely  sensation  ceases  when  the  hands 
or  feet  become  cold  ;  or  when  the  whole  body  is  labouring 
under  a  shivering  fit.  As  to  its  origin,  there  has  been  a 
great  diversity  of  opinion  ;  and  the  general  failing  arises  in 


3? 

making  it  too  particular.     No  doubt    I  think  should  be 
entertained,  as   to   its   resulting  from  chemical  changes, 
when  the    same   can  produce  it  out  of  the  body.      But 
we  cannot  suppose  that  these  are    the  only  sources,      A 
flush  of  confusion,    or    anger,    will  throw  the   face  and 
neck  into  a  glow  ;  but  here  it  is  absurd  to  introduce  chemi- 
cal changes.     Such  phenomena  seem  more  referrible  to 
the  nerves,  or  rather  their  irritability.     This  excitement 
may  even  depend  upon  physical  causes,  without  entitling 
us  to  draw  such  conclusions.     It  is  the  property  of  alcohol, 
when  tasted  to  act  on  the  nerves  so  as  to  produce  a  sen- 
sation of  heat ;  the  same  is  felt  in  the  stomach,  and    no 
doubt  can  be  entertained  but  that  the  same  physical  pro- 
perty afterwards  affects  the  nerves  of  the  heart   and  arte- 
rial system  so  as  to  occasion  the  fever  from  intoxication. 
We  may  even  suppose  that  all  exciters  have  this  power 
over  the  nerves,  in  consequence  of  their  chemical  compo- 
sition ;  yet  it  does  not  follow  that  they  should  always  have 
chemical  action.     The  two  branches  of  a  pine  tree,  for 
instence,  though  constituted  upon  these  principles,  do  not, 
when  rubbed  together,  produce  heat  by  chemical  action. 
Most  of  the   animal  temperature    seems  occasioned  in  a 
similar  manner.  When  we  rub  a  benumbed  limb  it  becomes 
very  soon  glowing  with  heat ;  our  muscular  motions  always 
produce  the  same  ;  so  must  the  incessant  action  of  ths  heart 
and  arteries.     And  when  we  consider  that  the   same  hap- 
pens when  two  pieces  of  wood  or  stones  are  rubbed  to- 
gether, we  should  view  the  result  as  depending,  not  upon 
life  or  chemical  combinations,  but  upon   one  of  the  most 
common  material  properties.     The  observation  of  Craw- 
ford, upon  the  difference  of  capacity  for  caloric,  between 
venous  and  arterial  blood,  is  no  doubt  illustrative  of  a  uni- 
form supply,  but  cannot  be  considered   as   sufficient   to 
establish  a  theory  on  animal  heat. 


S3 


GALVANISM,  ELECTRICITY,  &2C. 

The  process  of  secretion  has  long  been  a  subject  of  in- 
vestigation; but  manifest  as  its  effects  are,  and  notwithstand- 
ing the  great  importance  which  the  nervous  system  appears 
to  have  during  its  complicated  stages,  no  facts  have  been 
brought  to  light  sufficient  to  illustrate  its  nature.  We  find 
the  greatest  variety  of  these  products  among  vegetables, 
yet  few  have  been  willing  to  credit  the  existence  of 
nerves  in  plants.  The  polypus,  also,  is  an  instance  among 
animals  where  the  process  of  assimilation  takes  place 
most  perfectly,  and  to  all  appearance  without  a  nervous 
system.  To  these  we  may  add  the  formation  of  the  um- 
bilical chord,  and  some  examples  of  foetuses.  M.  Le  Gal- 
lois  mentions,  in  his  treatise,  several  where  neither  brain 
nor  spinal  marrow  were  to  be  found.  Clark  (I  think)  re- 
lates in  the  early  part  of  the  Philos.  Trans,  an  example 
where  not  a  single  trace  of  nerves  could  be  found,  al- 
though bones,  flesh,  cartalage,  membranes,  &c,  were  dis- 
tinctly formed.  These  considerations  lead  us  to  view  the 
nerves  merely  as  constituting  an  apparatus  for  the  secreting 
agent;  but  without  which  that  agent  may,  in  some  in- 
stances, be  effectual.  Several  difficulties  will  occur  if  we 
regard  the  nervous,  or  even  any  other  division  of  the  vas- 
cular system  as  necessary  for  the  formation  of  animated 
matter,  and  therefore  most  probably  for  all  secretions. 
We  find,  for  instance,  that  all  the  corporeal  texture 
which  is  concerned  in  such  offices  have  blood  vessels 
which  supply  materials  for  secretion  as  well  as  others 
which  support  the  organ  itself;  now,  whether  nerves  be 
necessary  for  the  last  or  not,  we  must  suppose  such  a  mi- 


39 

nuteness  of  vascular  structure,  by  continuing  this  arrange- 
ment downwards,  as  will  evidently  be  absurd,  or  else  we 
must  draw  the  conclusion,  that  the  formation  of  animated 
matter  does  take  place  upon  principles  independent  of 
the  vascular  arrangement.  Let  us  illustrate  the  idea  by 
an  example,  which  will  at  once  be  allowed  applicable  to 
all  the  rest.  When  a  nerve  is  injected,  its  substance  is 
found  to  be  interwoven  with  minute  blood  vessels.* 
These  are  for  its  support ;  and,  according  to  the  general 
economy,  should  be  accompanied  with  nerves  for  the  pur- 
pose of  secreting  freshnervous  matter;  but, be  this  as  it  may 
the  coats  of  these  minute  blood-vessels  must  be  support- 
ed. How  is  this  effected  ?  If  by  another  and  minuter  vas- 
cular apparatus,  how  is  the  substance  of  this  last  secreted  ? 
Thus  we  will  be  driven  to  fancy  the  existence  of  blood 
vessels  and  nerves  as  small  as  it  is  possible  to  divide  mat- 
ter ;  and  even  here  the  dilemma  cannot  cease,  since  for  the 
very  last,  secretion  of  substance  will  be  as  requisite  as 
for  the  first  and  largest  set.  On  the  other  hand,  we  are 
led  to  think  that  secretions  can  proceed  from  the  blood  by 
the  influence  of  an  agent  not  necessarily  limited  to  the 
nervous  apparatus.  This  J  really  conceive  is  best  sup- 
ported ;  for  if  the  foregoing  descending  series  of  vascular 
arrangement  be  inadmissible,  then  there  appears  no  alter* 
native  but  to  suppose  that  the  smallest  set  of  nerves  and 
blood  vessels  had  their  solid  texture  formed  from  the 
blood  without  further  apparatus.  At  a  subsequent  part  of 
this  essay  it  will  be  in  place  to  state  experiments  which  go 
to  prove  that  arterial  tubes  with  their  ramifications  can  be 
formed  directly  from  the  blood  by  its  chemical  or  physical 
properties.     At  present  I  shall  rely  on  the  foregoing,  and 

♦Bell's  Anat.  2d  vol. 


40 

consider  nerves  and  vascular  structure  as  established  for 
convenience  more  than  from  absolute  necessity  in  the  pro- 
cess of  converting  the  blood  into  organized  matter.  Sup- 
posing then  that  the  nerves  are  mostly  for  the  purpose  of 
forming  a  perfect  conducting  apparatus,  we  must  approxi- 
mate nearer  to  the  true  nature  of  the  agent  transmitted, 
when  we  experimentally  become  acquainted  with  any 
which  has  the  property  of  readily  passing  through  the 
same  medium.  The  similarity  is  much  farther  heightened 
when  we  learn  that  this  last  is  a  powerful  chemical  agent. 
Such  a  one  is  galvanism,  (including  its  modifications  of 
electricity  and  magnetism.)  It  is  not  my  attention  to  pre- 
sent a  history  of  this  very  extensive  agent,  but  merely  to 
examine  some  of  its  greatest  claims  to  being  considered 
the  nervous  principle,  and  that  employed  in  the  formation 
of  animated  matter. 

Dr.  Galvani  of  Bologna,  as  early  as  1791,  published  his 
discovery,  that  the  muscular  fibre  of  frogs  could  be  instant- 
ly excited  by  transmitting  through  its  nerves  the  minutest 
quantities  of  electricity.  He  also  proved,  that  this  muscu- 
lar excitement  would  take  place  without  any  external  sup- 
ply of  electricity,  when  a  conductor  was  made  use  of  to 
connect  the  nerve  and  muscle,  but  that  no  such  result  ever 
occurred  when  new  conductors  were  substituted.  This 
discovery  was  clearly  sufficient  to  prove,  that  nerves  are 
among  the  best  conductors  of  electricity.  After  that  time 
inquiry  was  set  on  foot,  with  the  most  unreasonable  ex- 
pectations, and  was  in  turn  as  rapidly  abandoned  because, 
unfortunately,  experiments  did  not  warrant  every  scheme 
of  the  investigator.  Without  considering  that  the  functions 
of  life  depended  upon  numerous  co-operating  principles, 
it  was  idly  hoped,  that  they  might  be  regenerated  in  the 
inanimate  structure,  where  every  other  principle  was  ex- 


41 

tinct,  except  the  fictitious  one.  It  is  not  necessary,  how- 
ever, that  all  such  anticipations  should  be  satisfied,  in  order 
to  show  the  similarity  between  galvanism  or  electricity 
and  the  nervous  agent.  There  are  no  less  than  four  kinds 
of  fish,  which  have  a  natural  apparatus  in  their  bodies, 
capable  of  imparting  shocks,  not  only  similar  to  those  from 
a  Leyden  jar,  but  upon  similar  principles.  These  are  the 
torpedo,  the  gymnotus  electricus,  the  silurus  electricus,  and 
another  found  at  the  Comoro  Islands,  which  seems  of  the 
genus  Tetrodon.  In  each  of  these,  there  seems  to  be  a 
distinct  organization,  for  the  purpose  of  accumulating  and 
transmitting  electrical  power.  In  the  torpedo  this  struc- 
ture consists  of  perpendicular  columns,  reaching  from  the 
under  to  the  upper  surface  of  the  body.  Hence  on  the  prin- 
ciples applicable  to  the  opposite  poles  of  a  galvanic  bat- 
tery, this  fish  must  be  touched  so  as  to  make  a  circuit 
between  its  under  and  upper  surface.  Then  a  strong 
shock  will  be  felt  throughout  the  connection ;  but  only  a 
chilliness,  when  either  one  is  singly  touched  ;  here  we 
perceive  a  perfect  coincidence  as  to  principle.  In  a  very 
large  torpedo  one  electric  organ  was  found  to  consist  of 
eleven  hundred  and  eighty-two  columns,  each  with  a  diam- 
eter of  one  fifth  of  an  inch.  The  shock  which  is  given  by 
the  torpedo,  when  standing  in  the  air,  is  about  four  times 
as  strong  as  when  standing  in  water.  This  fact  shows  an- 
other similarity  •,  for  water  is  a  much  better  conductor  of 
electricity  than  air,  consequently,  in  the  latter  position, 
more  will  be  transmitted  by  a  conductor.  The  torpedo 
shock  is  interrupted  by  nonconductors  of  electricity,  and 
transmitted  through  those  that  have  the  power.  Even 
though  the  circuit  should  be  formed  by  several  persons 
joining,  the  shock  will  be  felt  by  them  all  at  the  same  time.* 

*  Walsh's  paper,  Phil.  Trans,  vol.  63. 

G 


42 

Dr.  G.  W.  Schilling,  in  1764,  made  experiments  upon  a 
torpedo  about  six  inches  long  and  one  thick.  The  account, 
though  it  seems  extravagant,  cannot  but  be  considered  as 
demonstrating  a  very  close  resemblance  between  the  power 
accumulated  by  this  fish,  and  magnetism,  which  appears 
to  be  a  modification  of  electricity. 

He  put  it  into  a  vessel  of  water  when  its  vigour  was 
greatest.  A  magnet  with  a  power  of  four  ounces  was  then 
applied  near  the  fish,  which  immediately  began  to  move 
about  with  violence,  though  not  touched.  The  desire  to 
escape  seemed  greatly  to  increase,  as  the  magnet  was 
brought  nearer.  The  magnet  was  then  placed  in  contact 
with  the  water,  and  the  torpedo,  after  slowly  approaching, 
and  at  times  endeavouring  to  escape,  at  last  adhered  to  it, 
like  a  piece  of  iron.  After  being  cautiously  removed  to 
some  distance,  it  recovered  the  power  of  motion,  but  was 
totally  incapable  of  giving  a  shock.  The  magnet  again 
attracted  it,  where  it  adhered  for  half  an  hour,  and  then 
spontaneously  fell  off,  evidently  debilitated  and  without 
the  power  of  giving  shocks.  It  is  also  stated,  that  after 
the  immersed  magnet  had  destroyed  that  power,  iron  filings, 
when  thrown  into  the  basin,  occasioned  its  restoration. 
Something  analogous  to  this  may  be  seen  in  the  human 
body,  during  the  paroxysms  of  neuralgia.  It  is  a  fact 
well  authenticated,  that  when  this  nervous  affection  attacks 
the  cheeks,  a  magnet,  by  being  kept  in  the  mouth,  has  the 
power  of  allaying  the  pain.  A  very  intelligent  physician, 
who  had  long  suffered  from  this  excruciating  disease,  re- 
marks, that  he  relied  upon  a  magnet  which  he  kept  in  his 
mouth  next  to  the  affected  cheek,  and  found  it  capable,  for 
a  time,  of  affording  him  perfect  rest,  but  that  afterwards 
when  that  influence  had  ceased,  being  led  by  analogy  to 
try  a  more  powerful  magnet,  the  result  proved  of  a  most 


45 

contrary  nature  ;  the  pain  returned  with  such  violence  upon 
every  application,  as  to  render  the  attempt  almost  insup- 
portable.* With  the  view  of  checking  this  nervous  disease, 
physicians  have  effectually  recommended  the  use  of  mag- 
netic belts. 

From  some  experiments  performed  by  Mr.  Todd,  it  is 
shown  that  the  shock  of  the  torpedo  passes  from  the  elec- 
tric organs  through  its  connecting  nerves.  An  incision  was 
made  round  the  circumference  of  both  organs,  so  as  to 
leave  no  attachment  between  these  organs  and  the  animab 
except  by  nerves  ;  under  such  circumstances  shocks  were 
received  as  powerful  as  before  the  operation.!  In  this  fish, 
therefore,  we  see  that  a  power  very  similar  to  the  electric, 
is  naturally  accumulated  and  transmitted  through  nerves 
as  conductors.  The  gymnotus  electricus  in  my  opinion 
establishes  their  identity. 

Cavallo  remarks,  that  "  the  strongest  shocks  of  the 
gymnoti,  which  were  exhibited  in  London,  would  pass 
through  a  very  short  interruption  of  continuity  in  the  cir- 
cuit. They  could  be  conveyed  by  a  short  chain  when 
stretched  so  as  to  bring  the  links  into  a  more  perfect  con- 
tact. When  the  interruption  was  formed  by  the  incision 
made  with  a  penknife,  on  a  slip  of  tinfoil  that  was  pasted 
upon  glass,  the  shock  in  passing  through  that  interruption 
showed  a  small  but  vivid  spark,  plainly  visible  in  a  dark 
room.  This  animal  showed  a  peculiar  property,  namely, 
that  of  knowing  when  he  could,  and  when  he  could  not, 
give  the  shock  5  for  if  non-conductors  or  interrupted  cir- 
cuits were  placed  in  the  water,  he  would  not  approach 
them  ;  but  as  soon  as  the  circuit  was  completed,  he  would 
approach  the  extremities  of  that  circuit,  and  immediately 

*  Dr.  Jones'  letter  to  Dr.  Rush.  t  Phil.  Trans,  for  1817. 


44 

give  the  shock."*  In  other  respects  this  animal  resembles 
the  torpedo  ;  so  also  do  the  remaining  two,  the  silurus  and 
that  from  the  Comoro  Islands  ;  but  less  is  known  of  them. 
I  have  been  particular  in  describing  these  facts,  because 
the j  furnish  the  most  manifest  exhibition  of  the  nervous 
energy,  and  prove,  at  the  same  time,  that  it  is  the  same  as 
the  electric,  galvanic,  or  magnetic.  We  can  hardly  have 
a  more  beautiful  illustration  of  physical  phenomena  sub- 
servient to  the  vital  economy.  They  do  not  result  from 
fortuitous  circumstances,  but  depend  upon  a  separate  struc- 
ture well  adapted  and  apparently  acting  upon  as  definite 
principles  as  a  galvanic  battery.  On  this  subject  Sir  Eve- 
rard  Home  remarked,  in  his  paper  on  secretion,  that  these 
arrangements  prove,  "  that  a  voltaic  battery  can  be  formed 
in  a  living  animal,  and  that  nerves  are  essential  for  its 
management,  for  in  these  fish,  the  nerves  connected  with 
the  electrical  organs  exceed  those  that  go  to  all  the  other 
parts  of  the  fish  in  the  proportion  of  twenty  to  one.  The 
nerves  are  made  up  of  an  infinite  number  of  small  fibres, 
a  structure  so  different  from  that  of  the  electrical  organ, 
that  they  are  evidently  not  fitted  to  form  a  voltaic  battery 
of  high  power;  but  their  structure  appears  to  Mr.  Davy 
to  adapt  them  to  receive  and  preserve  a  small  electrical 
power.''  In  the  same  paper  an  experiment  is  stated  which 
shows  that  the  animal  structure  when  detached  has  the 
power  of  accumulating  nervous  energy,  or  in  other  words 
of  forming  a  voltaic  battery.  When  the  two  hind  legs  of 
a  live  frog  have  been  recently  cut  off  from  the  body,  the 
muscles  of  both  will  be  excited  to  contractions  if  the  cir- 
cuit be  completed  by  making  each  crural  nerve  pass  across 
from  its  own  limb,  and  touch  the  muscular  part  of  the 
other  leg.t 

*  Elements  of  Philos.  )  Phil.  Trans,  for  1819. 


45 

Lagrave  states,  that  by  placing  alternate  layers  of  brain 
and  muscular  fibre  together,  and  separating  them  by  a 
porous  body  soaked  in  salt  water,  a  galvanic  pile  will  be 
formed,  having  the  usual  effects.*  Here  we  see  that  the 
composition  of  animated  matter  qualifies  it  to  accumu- 
late, under  certain  circumstances,  the  galvanic  influence, 
and  although  the  arrangement  of  the  parts  is  not  natu- 
rally so  regular  as  this  of  Lagrave,  the  experiment  just 
mentioned,  of  the  frog's  legs,  shows  that  the  natural  one 
is  sufficient.  We  thus  learn  that  galvanism  is  accumulated 
by  the  structure  alone,  both  during  and  after  life  ;  we  are 
also  aware  that  its  power  is  able,  according  to  its  extent, 
to  effect  the  most  varied  chemical  changes  ;  what  then,  I 
would  ask,  can  authorize  us  to  consider  that  this  power, 
when  excited  during  life,  does  not  occasion  new  chemical 
compounds  whenever  materials  are  presented  ?  Many 
circumstances  lead  us  to  give  credit  to  this  power  as  a 
secreting  agent.  We  know  its  influence  over  compounds, 
out  of  the  body ;  we  know  that  it  can  be  accumulated 
in  the  living  system,  and  though  there  should  not  be 
nerves  to  transmit  it,  yet  any  organic  compound,  as 
the  animal  fluids,  which  by  their  position  can  direct  it, 
or  concentrate  its  power  by  forming  circuits,  must  lead 
as  directly  to  changes  of  composition.  Nerves,  however, 
are  almost  always  present  in  the  greatest  abundance. 
Whatever  may  be  the  apparent  use  of  this  structure,  we 
know  that  whether  for  secretion,  motion,  or  sense,  all  are 
open  to  the  galvanic  influence.  But  it  may  be  asked,  if 
such  is  the  arrangement,  why  are  not  the  nerves  of  sense 
and  motion  constantly  giving  rise  to  secretions  ?  To  this 
it  may  be  answered,  that  one  circumstance  can  always 
prevent  them,  even  when  galvanism  is    excited  in  their 

*  Bostock's  History  of  Galvanism, 


46 

neighbourhood.  Under  all  circumstances  its  course  will 
be  through  the  shortest  circuit,  and  for  this  reason  most  of 
its  power  will  be  confined  to  the  same  extent.  This  we 
know  from  experiment.  If  the  knob  and  outer  surface  of 
a  Leyden  jar  be  touched  by  the  thumb  and  fore  finger, 
the  violence  of  a  shock  will  be  confined  to  their  extent, 
but  if  the  two  hands  be  substituted  for  the  thumb  and  fore 
finger,  we  will  feel  the  shock  in  the  arms  and  shoulders. 
To  confirm  this  further,  let  a  person  standing  behind,  place 
his  hands,  one  on  either  arm,  or  either  shoulder,  so  as  to 
form  a  second  circuit,  and  although  his  is  connected  with 
the  first,  yet  as  it  is  the  longest  of  the  two,  he  will  feel 
no  shock.  Hence  we  see,  that  if  one  or  more  anastamo- 
sing  branches  of  nerves  intervene  between  the  accumula- 
ted galvanism  and  the  nerves  of  sense  or  motion,  little  or 
none  of  its  influence  can  extend  to  them.  If,  however, 
these  nerves  of  sense  are  include d  within  the  circuit,  they 
transmit  galvanism  with  perfect  freedom  ;  and  what  is  still 
more  singular,  as  Fourcroy  observes,  impart  the  sensations 
of  smell,  flavour,  pain,  warmth  and  vision.*  Ritter,  also, 
states,  that  the  electricity  of  the  positive  pole  augments 
the  actions  of  life,  while  that  of  the  negative  diminishes 
them.  Tumefaction  is  produced  by  the  former,  depres- 
sion by  the  latter.  The  pulse  of  one  hand  in  contact  with 
the  positive  pole  for  a  few  minutes  is  strengthened,  and 
gives  the  sensation  of  heat ;  that  in  contact  with  the  nega- 
tive, is  enfeebled  and  gives  the  feeling  of  coldness.  When 
the  eye  is  positively  electrified,  objects  appear  larger, 
brighter,  and  real ;  while,  to  one  negatively  electrified, 
objects  seem  smaller,  less  distinct,  and  bluish. f  Even  the 
smallest  galvanic  action  has  the  power  of  strongly  affect- 

f  Connais.  CUem.  f  Ure's  Dictionary. 


47 

ing  these  nerves.  When  a  piece  of  silver  is  placed  be- 
tween the  upper  lip  and  gums,  and  a  piece  of  zinc  un- 
der the  tongue,  this  simple  apparatus  is  capable,  when- 
ever the  mouth  is  closed  so  as  to  bring  the  metals  in  con- 
tact, of  giving  a  sour  taste  to  the  tongue,  and  a  flash  of 
light  to  the  eye,  perceptible  in  a  dark  room.  Other,  and 
more  familiar  ones  have  been  noticed ;  but  it  is  not  my 
object  to  enumerate  them. 

The  influence  of  galvanism  on  muscular  motion,  through 
the  connecting  nerves,  is  far  more  striking.  Small  pieces 
of  zinc  and  silver  are  sufficient  to  convulse  the  limbs  of  a 
frog,  or  other  small  animal,  so  as  even  to  throw  them  from 
place  to  place ;  but  the  magnitude  and  intensity  of  such 
effects  have  never  been  illustrated  so  forcibly  as  upon  the 
human  body.  Few  can  read  and  credit  Dr.  Ure's  experi- 
ments upon  the  executed  convict  without  allowing  that  even 
if  our  vital  motions  are  regulated  by  an  unknown  agent, 
none  better  need  be  sought  after  than  that  of  galvanism. 
With  his  battery  he  made  the  dead  chest  heave  as  in  re- 
spiration— the  eyes  open  and  shut  with  the  motions  of  life, 
but  the  ghastliness  of  death ; — the  mouth  and  lips  ran 
into  distortions  as  true  and  impressive  as  when  prompted 
by  the  strongest  or  worst  passions,  and  the  whole  face  be- 
came impressed  with  characters  so  energetic  as  to  sicken 
the  bystanders,  and  force  them  to  withdraw.  The  hands, 
arms,  and  legs,  were  also  thrown  into  motion  far  beyond 
the  natural  power,  and  so  violent  as  to  baffle  all  muscular 
resistance.  Dr.  Ure  concludes  his  experiments  by  sta- 
ting his  belief,  that  if  blood  had  been  present  and  pro- 
perly arranged,  he  could  have  succeeded  in  establishing 
circulation.*     We  may  not  accede  to  his  conjecture,  since 

*  Ure's  Chem.  Dictionary. 


48 

more  parts  than  he  could  command  would  require  to  be 
set  in  motion;  but  we  cannot  doubt  about  the  galvanic  in- 
fluence being  capable  of  exciting  their  actions.  Many 
other  conditions  beside  motion  are  requisite  for  life,  and 
even  this  one  might  prove  too  imperfect  for  circulation, 
since  it  has  been  remarked  by  Bichat*  and  others  that  the 
voluntary  muscles  are  thus  excited,  beyond  comparison, 
much  more  than  those  which  are  not  under  the  will. 
When  persons  are  attacked  with  nervousness,  one  of  the 
most  singular  symptoms  is  the  erratic  muscular  motion  ; 
the  fingers  twitch  irregularly,  and  the  impulse  shoots  from 
part  to  part  like  the  coursing  of  lightning.  This,  in  effect, 
is  what  would  result  from  electricity  constantly  accumula- 
ting and  diffusing  itself  through  multiplied  conductors. 
Galvanism  seems  to  act  as  a  stimulus  to  the  muscular  fibre, 
and  its  effects  are  too  manifest  to  require  any  further  de- 
tail. 

I  shall  now  consider  its  agency  in  secretion. 

Dr.  Wilson  Philip  on  this  subject  makes  the  following 
observation :  "  I  cannot  help  regarding  it  as  almost  ascer- 
tained, that  in  those  diseases  in  which  the  derangement  is 
in  the  nervous  power  alone,  where  the  sensorial  functions 
are  entire  and  the  vessels  healthy,  and  merely  the  power  of 
secretion,  which  seems  immediately  to  depend  on  the  ner- 
vous system,  is  in  fault,  galvanism  will  often  prove  a  valu- 
able means  of  relief."!  With  this  view  he  administered 
it  in  cases  of  habitual  asthma,  and,  according  to  his  own 
words,  "  it  failed  to  give  considerable  relief  only  in  about 
one  tenth."  It  may,  however,  be  supposed  that  such  ap- 
plication only  restored  the  muscular  motions  necessary  for 
respiration  without  otherwise  promoting  the  involved  se- 

*  Treatise  on  Life.  t  Philos.  Trans,  for  1S17. 


49 

cretions.  In  other  experiments,  related  by  the  same  au- 
thor,* digestion  was  accomplished  by  the  galvanic  influ- 
ence ;  but,  if  we  regard  analogy  from  man,  the  extensive 
connection  of  the  par  vagum  and  fact  that  the  coeliac 
plexus  sends  off  branches  to  the  stomach,  render  it  uncer- 
tain whether  the  gastric  secretion  was  directly  effected  by 
passing  the  galvanic  influence  through  the  par  vagum  or 
branch  of  the  eighth  pair.  However,  Dr.  Philip  as  justly 
remarks,  the  "  identity  of  galvanic  electricity  and  nervous 
influence  is  established  by  these  experiments."  He  divi- 
ded the  par  vagum,  which  is  distributed  to  the  stomach  and 
subservient  to  digestion,  by  incision  in  the  necks  of  seve- 
ral rabbits.  After  the  operation,  it  was  found  that  the 
parsley,  which  they  had  previously  eaten,  remained  in  the 
stomach  without  alteration,  and  after  a  longer  time  the 
animals  died  apparently  from  suffocation.  Other  animals 
underwent  a  similar  division  of  the  par  vagum  ;  but  the 
galvanic  influence  was  applied  to  the  portion  below  the 
division, or  to  that  which  was  connected  with  the  stomach. 
This  was  done  by  touching  one  wire  to  the  divided  end, 
and  the  other  to  a  silver  dish  or  plate,  placed  closely  in 
contact  with  the  skin  of  the  animal  opposite  to  its  sto- 
mach. In  this  last  case  no  difficulty  of  breathing  took 
place,  and  after  the  galvanic  influence  had  been  continued 
twenty-six  hours,  the  parsley  was  found  to  be  as  perfectly 
digested  as  that  in  healthy  rabbits  fed  at  the  same^time. 
Their  stomach  also  gave  the  peculiar  smell  which  those  of 
healthy  rabbits  have  during  healthy  digestion.  Until  a 
more  definite  knowledge  is  obtained  concerning  the  desti- 
nation of  nerves  connected  with  the  stomach  of  a  rabbit, 
these  interesting  experiments  can  only  be  considered  as 
relating  generally  to  the  functions  of  the   stomach,  in* 

*  Inquiry  into  the  Laws  of  Vital  Functions. 

7 


50 

eluding  its  muscular  motions,  (which  seem  much  more  con- 
siderable in  herbiverous  than  camiverous  animals,*)  as 
well  as  its  office  of  secretion,  &c. 

Experiments  have  been  made  upon  blood  and  its  com- 
ponents in  order  to  imitate  by  galvanism  the  secreting  pro- 
cess, but  the  range  has  hitherto  been  very  limited.  This 
is  what  might  be  expected  when  we  consider  how  very 
unfavourable  any  arrangement  must  be.  By  subjecting 
blood  to  galvanism  scarcely  more  than  one  product  can 
result,  since  it  is  but  reasonable  to  suppose  that  whatever 
compound  is  produced  from  any  of  its  serum,  the  same 
must  be  produced  from  all  of  it.  Probably,  if  any  thing 
can  promote  a  variety  of  products,  it  will  be  more  likely 
to  follow  when  that  first  formed  from  blood  is  taken  and 
exposed  by  itself  to  the  galvanic  agency,  repeating  the 
same  operation  for  all  as  they  may  occur. 

Dr.  Philipt  states,  that  galvanism  changes  arterial  blood 
to  a  dark  venous  colour,  and  prevents  the  formation  of  a 
coagulum,  or  at  least  dissolves  it  when  formed.  The  same 
kind  of  blood  at  the  same  time,  and  under  all  similar  cir- 
cumstances, except  that  of  galvanism,  retained  its  florid 
colour,  and  coagulated.  Galvanism  also  produces  caloric, 
by  its  action  upon  arterial  blood,  but  none  when  operating 
on  venous  blood.  It  is  also  remarked  by  the  same  writer, 
that  venous  blood  suffers  no*  visible  alteration.  Whether 
this  be  strictly  correct  or  not,  we  should  be  inclined  to 
suppose  that  arterial  blood  has  much  more  matter  to  un- 
dergo changes  than  that  found  in  veins  ;  and  any  such  anal- 
ogy between  the  galvanic  and  nervous  agency  is  of  the 
utmost  importance  to  be  known.  When  we  consider  their 
obvious  similarity  we  feel  inclined  to  illustrate  one  by  the 
other.     May  it  not,  therefore,  be  supposed,  that  the  gal- 

*  J.  Bell's  Anat.  vol.  3.  t  Inquiry  into  the  Vital  Functions, 


51 

vanic  influence  in  the  body  over  arterial  blood,  during  the 
time  of  secretion,  impoverished  it  agreeable  to  the  gal- 
vanic analysis,  giving  out  caloric,  as  Mr.  Philip  has  shown 
it  does,  and  changing  its  colour  from  florid  to  a  dark  one, 
leaving  it  thus  characterized  to  enter  the  veins  ?     The 
resemblance  is  certainly  close,  for,  according  to  these  ex- 
periments, galvanism  could  effect  no  more  changes  on  the 
venous  blood.     It  is  to  be  observed,  however,  that  Sir 
Everard  Home,  in  his  paper,  entitled  "  Hints  on  the  sub- 
ject of  animal   secretions,"*  details  changes  effected  by 
galvanism  or  venous  blood.     Some  of  these  I  shall  now 
mention.     They  were  performed  by  Mr.  William  Brande. 
He  immersed  the  conductors  of  a  four-inch  double  plate 
battery,  into   four  ounces    of  fresh    drawn  venous  blood, 
keeping  up  its  natural  temperature  all  the  time.    The  bath 
was  composed  of  a  very  weak  solution  of  muriatic  acid. 
The  galvanic  influence  seemed  to  cease  at  the  termination 
of  a  quarter  of  an  hour.  When  examined,  "  the^lood  which 
had  surrounded  the  negative  wire,  was  of  a  deep  red  co- 
lour and  extremely  alcaline  ;  that  surrounding  the  positive 
wire,  was  slightly  acid,  and  of  a  brighter  hue.     In  this 
experiment,  the   coagulation  of  the  blood  was  not  materi- 
ally affected  by  the  electrical  power  alluded  to."     Dr. 
Philip,  states,    that   venous  blood   undergoes   no  visible 
change ;    but   Brande  observed,  that  its  colour  became 
brighter.  Hare,  in  his  work  on  the  stomach,  mentions  that 
electricity    prevents    the  blood  from     coagulating   after 
death ;  in  tBe  foregoing  experiment,  as  well  as  in  another 
performed  by  Mr.  Brande  on  the  venous  blood  of  a  deer 
pithed  for  the  express  purpose  of  preventing    coagula- 
tion, we  find  that  this  property  of  blood  manifested  itself, 

Phi  los.  Trans,  for  1809 


52 

although  under  the  influence  of  galvanism.  There  is  this 
difference  however,  that  Hare  alludes  to  a  shock  power- 
fully and  rapidly  pervading  the  system,  as  when  struck  hy 
lightning,  whereas  the  blood  in  Mr.  Brande's  experiments 
was  exposed  to  a  current  $  so  that  the  fluid  might  by  the 
latter  mode  manifest  its  property  previous  to  any  exten- 
sive changes. 

One  of  the  most  interesting  discoveries,  by  transmitting 
galvanism  through  the  animal  fluids,  is  that  they  all  con- 
tain albumen  which  is  soluble,  when  united  to  an  alkali^ 
and  that  their  coagulation  depends  upon  that  union  being 
destroyed.  Mr.  Brande  in  his  paper  on  albumen*  has  ex- 
amined this  property  in  several  fluids ;  and  finds  that  a 
very  small  galvanic  power  is  sufficient  to  effect  a  perfect 
coagulation  at  the  negative  pole,  even  where  the  albumen 
is  diluted  with  so  large  a  quantity  of  water  as  not  to  be 
detected  by  the  usual  tests.  By  the  experiments  mentioned 
in  Sir  Everard  Home's  paper,  before  alluded  to,  it  appears 
that  galvanism  has  the  power  of  separating  albumen  from 
the  blood,  or  its  serum;  by  one  degree  of  power  it  is  sepa- 
rated in  a  solid  form,  and  by  a  less  degree,  in  &  fluid  form. 
Hence  then,  there  seems  reasonable  ground  for  presuming 
that  this  agent  is  extensively  employed  in  producing  the 
different  animal  solids  and  fluids  from  the  blood,  since  ac- 
cording to  Mr.  Hachett's  experiments,  albumen  is  the 
principal  material  of  which  animal  bodies  are  composed.! 
Mr.  Home,  remarks  "that  the  structure  of  the  nerves  may 
fit  them  to  have  a  low  electrical  power,  which  can  be  em- 
ployed for  that  purpose,  and  as  such  low  powers  are  not 
influenced  by  imperfect  conductors,  as  animal  fluids,  the 
nerves  will  not  be  robbed  of  their  electricity  by  surround- 

*Philos,  Trans,  for  1809.  tPhilos.  Trans,  for  1800. 


53 

ing  parts."  We  have  also  noticed  that  a  low  power  is  best 
adapted  for  effecting  the  separation  of  albumen.  This 
power  will  even  be  effectual  when  the  most  delicate  elec- 
trometer is  incapable  of  affording  the  least  indication.*  I 
have  already  remarked,  that  animated  matter  is  occasion- 
ally formed  where  nothing  like  a  nervous  structure  has 
been  detected;  (see  commencement  of  this  section;)  there 
are  instances  also,  when  this  structure  seems  too  minute 
and  imperfect,  to  perform  such  a  function.  All  embryos 
are  of  this  nature.  In  eggs  the  evanescent  structure  can 
hardly  be  supposed  to  work  all  the  diversity  of  animated 
compounds,  which  are  found  to  accumulate  so  very  rapidly. 
Its  condition  is  isolated,  and  without  any  more  maternal 
assistance  than  can  be  obtained  from  a  common  baking 
oven  ;  we  find  moreover,  that  the  vital  action  is  for  a  long 
time  confined  to  a  mere  speck.  The  condition  of  em- 
bryos matured  in  the  womb  is  scarcely  better ;  they  all  have 
a  rapid  secretion  of  animated  matter,  while  their  most 
favourable  connexion  with  the  mother  seems  merely  for 
the  purpose  of  affording  blood.  Even  if  we  suppose  (as 
is  most  probable)  that  this  blood  does  not  circulate 
through  both,  but  that  the  mother  affords  nutriment 
which  enters  elaborated  into  the  foetal  circulation,!  still 
all  the  peculiar  products  constituting  true  secretion  must 
be  effected,  exclusively  in  the  embryo.  Plants  of  the  most 
perfect  nature  are  not  supposed  to  have  nerves  ;  how 
much  less  reason,  then,  must  there  be  for  denying  the  ex- 
istence of  such  a  system  in  the  circumscribed  seed  ?  yet 
the  energy  of  an  acorn  sends  forth  the  gigantic  oak.  We 
find  the  secreting  power  as  prominent  in  the  millet  seed 
as  in  the  garden  bean,  and  limits  far  below  the  microsco- 

*Mr.  Home's  paper  on  secretion.  t  Chapman  on  foetal  circulation. 


54 

pic  power,  include  hundreds  of  such  systems.  When  we 
consider  these  facts,  we  must  come  to  the  conclusion,  not 
only  that  secretions  whether  animated  or  not,  can  occur 
without  a  nervous  structure,  but  that  in  the  early  stages 
of  corporeal  existence,  there  is  a  universal  and  diffusable 
agent  employed  for  its  advancement.  Two  reasons  in 
particular  induce  us  to  consider  this  agent  as  electricity 
or  galvanism.  It  is  qualified  to  produce  compounds  of  the 
most  varied  kind,  and  its  supply  is  constant  throughout 
nature;  open  to  the  minutest  assemblage  of  organized 
substances,  without  requiring  any  vital  action  on  their  part. 
Dr.  Philip,  in  his  work  on  vital  functions,  suggests  the  agen- 
cy of  galvanism  at  such  times.  "  If  the  nervous  influence 
be  galvanism,"  he  remarks,  "  there  may  be  some  appara- 
tus in  the  uterine  system  for  collecting  and  applying  this 
agent,  which  is  every  where  diffused,  till  the  brain  and 
spinal  marrow  can  perform  their  functions ;  and  which 
may  continue  to  supply  their  place  where  they  never  exist. 
We  have  seen  that  galvanism  is  capable  of  performing  all 
the  functions  of  the  nervous  system,  properly  so  called. 
In  combination  with  the  powers  of  circulation,  it  can, 
therefore,  perform  all  the  functions  essential  to  the  life  of 
the  perfect  animal,  except  respiration,  for  which,  we  have 
seen  the  sensorial  power  (residing  almost  entirely  in  the 
brain)  is  necessary."  Elsewhere  this  writer  continues: 
"  we  must  regard  the  rudiments  of  life  as  confined  to  the 
circulation,  from  which,  by  the  power  of  galvanism  col- 
lected by  some  means  external  to  the  foatus,  all  other  parts 
are  gradually  evolved  ;  till  within  the  foetus  itself,  a  gal- 
vanic apparatus  of  sufficient  power  for  the  performance 
of  the    nervous  functions  is  produced."*     However  we 


55 

may  revolt  from  terms  and  expressions  which  give  the 
vital  functions  the  appearance  of  depending  upon  combi- 
nations, which  we  can  only  accomplish  by  mechanism  ; 
we  should  always  recollect  that  the  principle  is  distinct 
from  the  workmanship ;  and,  I  must  confess,  I  am  aware 
of  no  illustration  so  apt  on  the  present  occasion  as  galvan- 
ism; no  matter  whether  the  womb  be  the  apparatus  or 
the  embryo,  or,  indeed,  the  universe  itself. 

LIGHT. 

The  agency  of  this  principle  over  the  vital  functions, 
and  of  course  over  the  animated  productions,  is  in  a  num- 
ber of  instances  very  obvious  and  important.  It  is  proba- 
ble, however,  that  its  extensive  influence  depends  upon  its 
being  a  compound  of  two  of  the  most  active  ones  before 
mentioned.  The  solar  light  is  the  form  alluded  to  in  the 
present  consideration  ;  and  we  learn  from  the  prismatic 
analysis,  that  the  sunbeam  is  composed  of  rays  of  colour? 
heat,  and  electricity.  The  first  does  not  seem  capable  of 
effecting  chemical  changes,  and  the  two  latter  have  already 
been  noticed.  But  as  the  action  of  sunshine  is  very  re- 
markable, and  as,  in  the  present  state^of  knowledge,  it  is 
impossible  to  explain  its  peculiarities  by  the  properties  of 
any  constituent  aloney  I  have  assigned  a  separate  considera- 
tion for  the  agency  of  life. 

Sir  Humphry  Davy*  remarks,  that,  "  in  general,  in  na- 
ture the  effects  of  the  solar  rays  are  very  compounded* 
Healthy  vegetation  depends  upon  the  ^presence  of  the 
solar  beams,  or  of  light ;  and  whilst  the  heat  gives  fluidity 
and  mobility  to  the  vegetable  juices,  chemical  effects  like- 
wise are  occasioned,  oxygen  is  separated  from  them,  and 

*  Elements  of  Cbem.  Philos-. 


56 

inflammable  compounds  formed.  Plants  deprived  of  light 
become  white,  and  contain  an  excess  of  saccharine  and 
aqueous  particles  ;  and  flowers  owe  the  variety  of  their 
hues  to  the  influence  of  the  solar  beams.  Even  animals 
require  the  presence  of  the  rays  of  the  sun ;  and  their 
colours  seem  materially  to  depend  upon  the  chemical  in- 
fluence of  these  rays.  A  comparison  between  the  polar 
and  tropical  animals,  and  between  the  parts  of  their  bodies 
exposed,  and  those  not  exposed  to  light,  shows  the  correct- 
ness of  this  opinion."  In  the  animal  creation,  brilliancy  of  co- 
lour and  gaudy  plumage  belong  to  the  tropical  climates ;  more 
sombrous  tints  distinguish  thepolarinhabitants  j  and  dull  co- 
lours characterize  nocturnal  animals,  and  those  who  chiefly 
abide  below  the  surface.*  In  detailing  the  properties  of 
light  on  the  living  system,  I  shall  be  compelled  to  neg- 
lect all  arrangement  or  connexion  ;  the  subject  does  not 
admit  of  it.  The  effects  of  light  are  moreover  of  such  a 
general  nature,  that  it  will  be  impossible  to  point  out  its 
immediate  agency  in  the  production  of  animated  substances. 
Indeed,  there  is  reason  to  suppose  that  it  has  none,  since 
their  formation  generally  takes  place  within  the  corporeal 
system.  But  its  importance  in  many  of  the  functions  con- 
ducive to  such  formations,  cannot  be  overlooked.  The 
action  of  light  on  animals  is  not  so  well  understood  as 
upon  vegetables.  We  find  that  oviparous  animals  gene- 
rally deposit  their  eggs  or  spawns,  where  they  will  be  ex- 
posed to  the  sunshine.  One  great  source  of  vitality  re- 
sulting from  this  arrangement  is  the  warmth  induced. 
Indeed,  we  may  suppose  this  to  be  the  prominent  advan- 
tage, since  we  find  birds,  as  the  ostrich,  deposit  their  eggs 
in  sand  banks,  which  as  well  as  the  egg  shell  itself  has  the 
power  of  reflecting  light ;  and  in  the  night  time  the  agency 

*  Brande*s  Chem. 


57 

of  light  seems  withdrawn,  whereas  that  of  warmth  still  re- 
mains   Besides,  the  hen  and  other  birds  which  set  on  their 
eggs  so  great  a  portion  of  time,  must  prevent  the  access  of 
light,  while  at  the  same  time  they  accumulate  the  range  of 
temperature.     In  vegetables  the  advantange  of  sunsnineis 
very  manifest.     Plants  growing  in  hot  houses  wih  expose 
their  leaves  to  the   sunshine,  although   the   quality  of  the 
circumambient  air  cannot   be  materially  altered,  sinr-.e  the 
light  enters  by  glass  casements ;  neither  does  its  tempera- 
ture require   any  farther  increase.     This  appetence  is   in 
some  instances  very  remarkable.     Light  acts  beneficently 
upon  the  upper  surface  of  leaves  and  hurtfully  upon  the 
under  side.     This  at  least  applies  to  most  plants,     What- 
ever  be  their  situation,  either  nailed  up  against  a  north  or 
south  wall,  impending,  or  in  a  hot  house,  they  will  invaria- 
bly turn  to  light  the  side    of  the  leaf  that  (m  a  perpendi- 
cular position  of  the  plant)  is  uppermost ;  even  when   by 
such  motion  less  heat  comes  to  them,  as  in  a  hot  house. 
So  great  is  this  power,   that  though   repeatedly  checked 
by  forcible  retrograde  motion,  the  leaves  will  constantly 
turn  back  again,  until  the  plant  becomes  weak  as  it  were 
by  exertion.     The  misletoe  and  some  others,  both  sides  of 
whose  leaves    are   alike    in    appearance ;   or    the  upright 
sword-shaped    leaves,   both    sides     of    which    seem     to 
perform  the    same  function  with  light,  are    indifferently 
exposed,  and  do  not  alter  in  consequence  of  any  variation 
of  the  light,  or  of  the  position  among  the  stem  and  branch- 
es.    A  familiar   example   of  leaves  following    the  sun  and 
its  beams,  may  be  observed  in  a  clover  field.     The  Helia- 
anthus  anneas,  or  sun  flower,  turns  with  its  biossom  all 
day  to  follow  the  sun  ;  and  at    night,   retraces  the  same 
course  to   meet  him  as  he  emerges,  in  the  morning,  from 
the  east.     Calandrini  found  that  vine  leaves  turned  to  the 


58 

light  when  separated  from  the  stem  and  suspended  by  a 
line  thread.*  This  last  observation  seems  to  show,  that 
the  important  agency  of  light,  though  constituting  a  vital 
phenomenon,  is  effected  upon  physical  principles. 

I  shall  now  examine  what    are  the  changes  effected. 
Priestley,  in  1778,  observed  that  plants,  under  certain  cir- 
cumstances, emitted  oxygen  gas.t    Ingenhausz  afterwards 
determined,   that   the  leaves  performed  this  function  and 
only  at  such  times  as  the  sun's  light  shines  full  upon  them. 
Thus  it  was  found  that  when  the  leaves  of  a  plant  were 
made  to  pass  under  into  a  glass  receiver,  inverted  and  full 
of  water,  that  the  upper  surfaces  gave  bubbles  of  oxygen 
gas,  as  long  as  the  sun  shone  on  them.j     This  effect  seems 
to  follow  chiefly  from   the   agency  of  light.     Subsequent 
experiments  proved,  that  it   was  not  the  water  which  be- 
came decomposed  ;   since  no  bubbles   appear  when  that 
fluid  has  been  boiled  ;  but  that  they  depended  upon  carbo- 
nic acid  gas,  dissolved  by  the  water,  and  that  their  number 
will  be  in  proportion  to  the  quantity  of  that  gas.§     Hence 
then  from   these  data   we  learn  the  agency   of  sunshine. 
Water  is  not  decomposed  to  any  extent,  whereas  oxygen 
gas  is  liberated,  therefore  the  carbonic  acid  must.  The  plant 
retains  one  of  the  constituents  (carbon)  for  its  nourishment; 
while  the  other  (oxygen)  is  set  at  liberty  and  rises  in  the  bell, 
hi  the  dark  it  is  found  that  plants  reverse  this  operation; 
that  is,  they  give  out  carbon  and  absorb  oxygen.     But  the 
extent  at  this  time  is  very  trifling.     Otherwise  the  carbon 
taken  in  for  nourishment  during  the  day  would  be  lost 
during  night,   (particularly  in  those  sections  of  the  earth 
where  the  night  nearly  equals  the  day,)  and  the  plants  ul- 
timately decline.     This  result  would  be  contrary  to  obser- 
vation ;  and  as  it  is,  we  perceive  how  plants,  upon  the 

Smith's  Botany,    t  On  air.    |  On  vegetation.    §  Encyc.  Method.  Physiol. 


59 

whole,  conduce  to  the  general  economy  by  subtracting 
carbon  from  the  carbonic  acid  of  the  atmosphere,  and  re- 
placing it  by  oxygen  gas,  which  is  so  essential  to  the  life 
of  all  animals.  Sunlight  has  a  very  considerable  deoxi- 
dizing powers  as  may  be  seen  by  exposing  nitrate  of  sil- 
ver to  it  for  a  short  time.  The  salt  will  be  decomposed, 
and  this  results  in  consequence  of  the  light  subtracting 
oxygen.  But  carbonic  acid  is  not  so  easily  decomposed 
by  this  single  power,  so  that  we  may  consider  the  above 
to  be  effected  by  two  affinities,  depending  both  upon  the 
plant  and  light.  The  nature  of  the  agency  of  light  is 
shown  by  another  experiment.  When  plants  are  exposed 
to  hydrogen  in  the  dark,  they  still  remain  green ;  though 
without  this  gas  the  absence  of  light  would  occasion  that 
green  to  become  a  faded  white  colour.*  Hydrogen  gas 
has  its  most  powerful  affinity  for  oxygen;  and  the  simila- 
rity of  effects  intimates  that  light  also  exerts  the  same 
kind  of  agency.  From  this  experiment  we  might  be  led 
to  suppose  that  the  green  colour  depends  in  some  manner 
upon  the  supply  of  carbon.  We  find  that  when  the  sun 
shines  upon  a  plant  carbon  is  readily  obtained  from  at- 
mospheric carbonic  acid,  and  the  colour  becomes  fresh 
and  green.  The  presence  of  hydrogen  is  able  to  produce 
the  same  effect,!  apparently,  because  it  takes  the  oxygen 
of  carbonic  acid  and  leaves  the  carbon  to  unite  to  the 
plant.  But  in  the  dark  no  carbon  is  furnished,  since  there 
is  no  effectual  agent  present,  and  the  plant  loses  its  green 
colour,  and  fades  to  a  whitish  one.  With  these  remarks  I 
shall  conclude  the  subject  of  light ;  since,  as  has  before 
been  observed  the  range  of  experiment  is  by  far  too  limit- 
ed to  give  much  information  upon  the  peculiarities  of  its 
agency. 

*  Smith's  Botany.  t  Thompson's  Chem.  vol.  4. 


60 


atmospheric  air.  [Oxygen.) 

It  is  well  known  that  the  vital  functions  cannot  long 
continue  without  the  assistance  of  this  air.  It  follows, 
therefore,  that  the  formation  of  animated  matter  absolute- 
ly depends  upon  it  or  some  other  possessed  of  similar  pro- 
perties. It  will  not,  therefore,  be  necessary  to  dwell  long 
on  this  point ;  as  the  nature  of  its  agency  is  of  most  im- 
portance. The  experiments  of  Ray,  Boyle,  Muschen- 
broeck,  and  Boerhaave,  all  prove,  beyond  a  doubt,  that  no 
plant  vegetates  in  the  vacuum  of  the  air  pump.  It  follows, 
therefore,  that  no  seed  will  germinate  unless  atmospheri- 
cal air,  or  some  air  having  similar  properties,  have  access 
to  it ;  and  it  is  for  this  reason  that  seeds  will  not  germi- 
nate at  a  certain  depth  below  the  surface  of  the  earth.* 
Guided  by  similar  phenomena,  the  agriculturist  finds  that 
ploughing  the  soil  is  the  surest  way  to  destroy  weeds  and 
grasses  ;  by  which  process  the  sod  is  turned  over  on  them, 
and  they  become  hid  from  the  air  in  consequence  of  being 
hid  in  the  furrow.  It  is  now  determined  that  it  is  the 
oxygen  in  atmospheric  air  which  is  of  such  importance  ; 
and  that  no  seed  will  germinate  in  any  other  gas  unless 
mixed  with  it.  An  experiment  of  Mr.  Humboldt  corrobo- 
rates this  very  beautifully.  This  gentleman  found  that 
seeds  vegetate  more  rapidly  when  steeped  in  a  solution  of 
chlorine;  and  it  is  the  distinguished  property  of  this  sub- 
stance to  liberate  oxygen  by  decomposing  water.  At  Vi- 
enna, seeds  which  had  been  long  kept,  and  which  had  con- 
stantly refused  to  germinate,  grew  readily  when  treated 
with  it.t  In  the  commencement  of  germination,  if  under 
favourable  circumstances,  carbonic  acid  is  given  off  for  a 

*  Ann.  de  Chim.  iii.  57.  t  Thompson's  Chem.  vol.  4. 


€1 

time,  even  when  no  oxygen  gas  is  present.  This,  therefore, 
seems  to  result  from  an  internal  chemical  action   convert- 
ing the  iarrinaceous  matter  of  the  cotyledons  into  saccha- 
rine and  other  nutritive  matter.     We  see  a  similar  phe- 
nomenon in  the  malting  of  grain,     It  seems,  from  experi- 
ment,  that  the  water  at  such  times  is  not  decomposed, 
since   neither   oxygen  nor   hydrogen   is    liberated.     But 
when  the  cotyledons  have  afforded  their  substance  for  sup- 
port, the  presence  of  oxygen  becomes  absolutely  neces- 
sary ;  and  as  much  carbonic  acid  (in  bulk)  is   found  as 
there  is  oxygen.     This  seems  nearly  all  the  use  of  oxygen 
gas  at  such  times,   because  as  the  carnonic  acid  is  just 
sufficient  to  require  the  whole  quantity,  none  can  be  im- 
bibed by  the  see  is.     They,  on  the  contrary,  by  such  a  pro- 
cess, lose  carbon.     Saussure  determined  that  wheat  and 
barley  consumed  oxygen  in  this  manner  between  ^V o  an(^ 
^  of  their  weight ;  whereas  beans  required  as  much  as 
1^T.     Hence  we  see  plainly  that  the  quantity  varies  to  a 
great  extent  according  to  the  kind  of  seed.     In   these  in- 
stances beans  seem  to  require,  at  least,  ten  times  as  much 
oxygen  as  wheat  and  barley.     A  comparison  of  the  expe- 
riments here  detailed,  with  those  mentioned  when  treating 
of  light,  point  out  a  singular  difference  between  the  econo- 
my of  a   seed  and  that  of  a    plant.     The  former  (seed) 
seems  to  require  the   emission  of  carbonic  acid,  while  the 
latter  decomposes   carbonic  acid  and  retains  its  carbon. 
It  is  true  they  are  under  very   different   circumstances, 
since  the  plant  effects  these  changes   by  the   agency  of 
light,  whereas  the  seed  is  deprived  of  it.     It  is  true,  also, 
that  plants  themselves,  when  in  the  shade,  seem  to  emit 
carbonic   acid.*     But  under  the  circumstances  most  ad- 
vantageous to   each   this  difference  evidently  exists.     It 

*  Ingenhausz  on  Vegetation. 


62 

has  been  shown  that  plants  cannot  thrive  without  oxygen  ; 
and  Saussure,  in  his  researches  on  vegetation,  discovered 
that  in  the  day  time  they  give  it  out,  (chiefly  taken  from 
the  carbonic  acid  which  is  absorbed  by  them  for  the  pur- 
pose of  subtracting  its  carbon,)  and  in  the  night  they  take 
in  a  fresh  supply.  It  would  be  useless  to  detail  all  such 
peculiarities ;  those  already  noticed  are  sufficient  to  show 
the  general  agency  of  oxygen  gas  or  atmospheric  air ;  and 
almost  all  the  important  facts  on  this  subject  may  be  found 
amply  noticed  by  Dr.  Thompson,  in  his  system  of  chem- 
istry, vol.  4. 

The  presence  of  oxygen  gas,  after  respiration  has  com- 
menced, is  justly  considered  as  indispensable  ;  but  its  utility 
during  all  the  previous  changes  of  animal  existence,  is  as 
yet  very  much  overlooked.  I  think  there  can  be  no  doubt 
but  that  one  general  principle  governs  both  vegetable  and 
animal  formation,  and  that  whenever  such  operations  take 
place,  whether  in  the  adult  or  embryo,  the  same  agents 
are  directly  or  indirectly  employed.  Dr.  Ewell,*  made 
experiments  which  show  the  importance  of  oxygen  gas  at 
this  early  period  of  animal  existence.  He  ascertained, 
that  the  semen  of  man  owes  its  fluidity  to  oxygen ;  or  rather 
that  it  absorbs  this  gas,  and  then  becomes  fluid.  He  remarks 
that  "  after  making  several  experiments,  and  reflecting  on 
the  subject,  he  is  convinced  that  the  presence  of  pure 
vital  air,  or  oxygen  gas,  is  necessary  to  give  the  first  ani- 
mation to  the  embryo  formed  in  the  uterus.  That  it  is 
only  after  this  union,  with  a  little  oxygen,  that  the  embryo 
is  enabled  to  receive  nutriment  from  the  mother,  and  that, 
consequently,  coition  will  always  be  unfruitful  unless  it 
takes  place  in  pure  air."  Whatever  may  be  the  agency  of 
oxygen  gas  upon  the  embryo  in  the  womb,  it  is  manifest  that 

*  Letters  on  Generation,  Med.  Repos.  No.  38, 


63 

its  supply,  per  vaginam,  must  be  very  limited.  Dr.  Ewell, 
states  another  of  his  experiments,  which  may  be  considered, 
however,  as  relating  more  to  the  changes  necessary  for 
nourishment,  than  as  proving  the  nature  of  incipient  anima- 
tion. "  Two  frogs  engaged  in  copulation,  were  taken  and 
held  in  vessels  containing  pure  distilled  water;  one  vessel 
of  water  was  impregnated  with  nitrogen  gas,  another  with 
carbonic  acid  gas,  a  third  with  atmospheric  air,  and  a  fourth 
with  oxygen  gas.  In  each  of  these,  the  frogs  deposited  their 
filaments  which  was  carefully  attended  to,  for  several  days. 
It  was  found  that  only  the  filaments  in  the  vessels  contain- 
ing oxygen  and  atmospheric  air,  had  the  least  appearance 
of  tadpoles."  Other  facts  are  stated,  by  Dr.  Ewell,  apper- 
taining to  propagation.  They  may  be  seen  in  his  letter  to 
Dr.  Miller.*  Bird's  eggs  are  constructed  so  as  to  be  sup- 
plied with  atmospheric  air  or  its  constituent  oxygen  gas. 
They  have  all  at  the  but  or  large  end  a  pouch  called  the 
folliculus  eeris,  for  the  purpose  of  containing  the  air.  The 
vitellus  or  yolk,  as  appears  by  the  hen's  egg,  is  so  poised 
by  thin  menbranes,  that  the  cicatricula  (very  near  which 
the  func turn  saliens,  or  first  point  of  animation  is  observed) 
may  always  face  upwards.  This  is  effected  by  the  orga- 
nization, which  makes  that  portion  of  the  vitellus,  which  is 
opposite  the  cicatricula  and  outside  the  line  of  suspension, 
the  heaviest ;  and  it  has  two  prominent  advantages.  It 
always  keeps  the  neighbourhood  of  the  functum  saliens  (in 
every  position  of  the  egg)  nearest  to  the  two  great  chemical 
agents,  caloric  and  vital  air.  The  first  is  furnished  by  the 
hen  bird,  and  the  last  by  the  follicle  or  air  bag.  Whatever 
be  the  shape  or  kind  of  egg,  this  arrangement  will  occasion 
such  approximation ;  generally  the  air  is  collected  in- the 
but,  because  this  end   is  the  highest.     During  incubation 

*Med.  Repos.  No.  38. 


64 

there  is  a  still  closer  approach  of  the  vitellus  to  the  folli- 
culsts'  sens.  It  is  not  necessary  to  attribute  this  phenome- 
non to  a  vital  power ;  since  it  takes  place  m  consequence 
of  chemical  changes  rendering  the  yolk  specifically  lighter. 
Indeed,  it  extends  the  truth  that  nature  makes  a  liberal 
use  of  her  physical  laws  even  in  the  very  foundation  of 
life  ;  and  it  is  even  proved  that  when  the  egg  is  kept  up- 
right on  its  but,  the  vitellus  will  rise  to  the  point,  and  thus 
leave  the  follicule.*  By  the  natural  position,  however,  it 
is  manifest,  that  though  still  guided  by  the  same  laws  they 
must  approach  each  other. 

Dr.  Paris,  in  his  memoir  on  the  physiology  of  the  egg,f 
gives  the  following  description.  "  The  external  shell  and 
the  internal  membrane  with  which  it  is  lined,  constitute 
the  varieties  of  the  folliculus  seris  ;  its  extent  in  the  recent 
egg  is  extremely  small,  and  before  its  exclusion  from  the 
uterus,  it  does  not  appear  to  exist.  It  would  seem  to  com- 
mence at  the  moment  the  egg  is  deposited  by  the  bird. 

A  small  portion  of  the  watery  contents  of  the  egg 
transpire  through  the  shell,  and  the  air  then  rushes 
through  the  obtuse  end,  and  inflates  the  follicule,"  &c.  "Its 
size  and  subsequent  increase  are  to  be  explained  upon  the 
same  principle  ;  which  they  establish  an  important  rela- 
tion between  the  diminution  of  the  bulk,  of  the  ovular 
contents  and  the  extent  of  this  preumatic  apparatus.  Dur- 
ing the  progress  of  incubation,  it  is  dilated  to  a  very  con- 
siderable magnitude."  A  few  days  after  incubation,  blood 
vessels  are  observed  to  "  extend  and  multiply  their  rami- 
fications on  the  yolk  and  white,  by  which,  the  blood  is  ex- 
posed to  the  action  of  the  air  in  the  follicle,  oxygenated 
and  returned  to  the  embryon."     This  use3  Dr.   Paris  re- 

*  Barr's  Buffon,  vol.  3.  page  24,  t  Ann.  Philos.  for  1821. 


65 

marks,  is  manifested  by  the  position  of  the  blood  vessels, 
as  well  as  by  the  air  itself,  which,  before  incubation,  is 
atmospheric,  but  which  afterwards  becomes  contaminated 
with  carbonic  acid  gas.     The  increase  which  this   air  at 
the  but  of  a  hen's   egg  obtains  by  incubation,  is,  accord- 
ing to  Dr.  Paris,  as  nearly  ten  to   one.     Whatever  ob- 
structs the  inflation  of  this  follicle  and  the  renewal  of  its 
air  destroys  the  embryo.     The  experiments  of  Reaumur 
offer  abundant  proof  of  this  truth.     In  his  attempts  to  de- 
velope  the  egg  by  the  heat  of  dung,  they,  for  a  long  time, 
failed,  owing  as  the  subsequently  discovered,  to  the  im- 
purity of  the  atmosphere.     He  also  varnished  eggs,  so  as 
to  prevent  the  access  of  air ;  and  found   that  when  such 
were   placed  under  the  hen,    they    invariably  perished. 
Spallanzani  instituted   many  experiments  with  the  same 
view.     "  I  have  often,"  says  he,  "  placed  the  eggs  of  ter- 
restrial and  aquatic  insects  under   the  receiver  of  an  air 
pump  ;  but  none  ever  hatched  in   this  situation,  although 
in  every  other  respect  in  a  condition  to  do  so."     Boer- 
have  also  remarks,     that  "  ovula  quorum  cunque  insecto- 
rum,  in  vitris  accurate  clausis,  non  producunt"     It  is   a 
fact  well  known  in  the  farm  yard,  that  turkeys  frequently 
destroy  or  smother  their  eggs  by  a  too  constant  and  assi- 
duous attention. 

Dr.  Paris  then  proceeds  to  notice  that  the  air  follicule 
may  also  have  a  secondary  office  to  perform,  namely, 
that  of  producing  by  its  air  a  part  of  those  necessary 
chemical  changes  which  the  albumen  and  vitellus  are 
found  to  undergo.  It  will  not  be  necessary  to  extend  this 
inquiry  ;  we  see  plainly  the  importance  of  oxygen  gas,  or 
atmospheric  air  for  all  kinds  of  embryos ;  and  the  animal 
as  well  as  vegetable  one  seems  to  require  the  supply  for 
the  purpose  of  getting  rid  of  carbon.     The  adult  animal 

9 


66 

still  displays  the  same  economy  ;  but  plants  seem  to  give 
out  carbon  only  in  the  night  or  shade,  and  then  in  exceed- 
ingly small  quantity.*  When  treating  of  respiration  as  a 
part  of  the  process  of  sanguification,  I  shall  take  up  the 
consideration  of  oxygen ;  also,  subsequently  when  examin- 
ing irritability  as  a  property  of  animated  matter.  For  the 
present  it  will  be  sufficient  to  remark,  that  oxygen  gas  is 
intimately  concerned  in  every  vital  function,  both  animal 
and  vegetable,  wherever  assimilation  or  secretion  is  per- 
formed. 

AGENTS    IN    GENERAL. 

I  have  been  led  to  include  atmospheric  air  among  che- 
mical agents ;  because  its  presence,  which  is  almost  uni- 
versal, always  promotes  changes  of  composition.  But 
upon  an  examination  it  will  be  perceived  that  its  influence 
depends  merely  upon  presenting  a  substance,  (oxygen) 
which  has  a  strong  chemical  affinity  for  most  other  organic 
substances.  It  certainly  has  no  power  of  itself  to  dispose 
bodies  to  union ;  which  is  the  strict  signification  of  an  agent. 
On  the  contrary,  it  may  be  considered  in  the  very  oppo- 
site point  of  view ;  for  it  is  evident,  that  if  the  atmospheric 
pressure  were  taken  off  from  all  bodies  there  would  be 
more  aeriform  states,  and  therefore  more  chemical  com- 
binations. In  noticing  the  vital  function,  we  are  often  led 
to  consider  bodies  as  agents,  when  in  truth  their  influence 
depends  upon  presenting  materials  with  strong  chemical 
affinities.  The  gastric  juice  is  most  generally  called  an 
agent ;  but  if  it  is  at  all  so,  it  must  depend  upon  being  a 
solvent,  or  upon  possessing  some  of  those  mentioned  pre- 

*  Thompson's  Chem.  vol.  iv.  Vegetation. 


67 

viously  to  atmospheric  air.  So  also  we  might  regard  ex- 
ercise, appetite,  disease  or  violent  injuries,  as  agents,  since 
they  all  predispose  the  body  to  a  new  series  of  chemical 
changes.  Guided  by  such  considerations,  it  is  evident 
that  the  number  of  agents  would  be  unreasonably  and  in- 
finitely extended.  I  shall  therefore  pass  over  their  con- 
sideration, and  treat  of  alteratives,  which  are  the  most 
notable  of  the  kind. 

ALTERATIVES. 

By  this  term,  I  mean  all  such  substances  as  have  the 
power  of  producing  an  alteration  in  the  irritable  action  of 
animated  matter.  There  is  no  name  expressive  of  such  a 
class  of  bodies,  unless  it  be  this  one.  I  shall  not,  there- 
fore, dwell  on  its  merits,  but  proceed  with  its  present  ap- 
plication. Alteratives  are  either  mechanical  or  chemical; 
but  the  nature  of  my  subject  leads  me  to  the  considera- 
tion of  the  latter.  I  must  remark,  however,  that  the  for- 
mer kind  act  a  highly  important  part  in  the  animated  body. 
All  distensions  of  the  heart,  womb,  bladder,  and  other  vis- 
cera, appear  of  this  nature.  Mechanical  alteratives,  by 
their  size,  figure,  or  weight,  may  lead  almost  directly  to 
chemical  decomposition. 

Chemical  alteratives  consist  of  such  bodies  as  affect  ir- 
ritability by  their  peculiarity  of  composition.  Arsenious 
acid  (white  arsenic)  will  illustrate  the  distinction.  By  its 
weight,  size,  or  irregularity  of  shape,  it  is  always,  in  the 
first  instance,  a  mechanical  alterative  ;  but,  by  its  qualities 
of  composition,  which  are  evidently  unconnected  with  the 
foregoing  properties,  it  acts  as  a  chemical  alterative. 

Chemical  alteratives  are  divided  into  sedatives  and  sti- 
muli.   The  former  are  supposed  always  to  diminish  the 


extent  of  irritable  action,  and  the  latter  to  augment  it. 
This  distinction  arises  from  their  ultimate  effects ;  but  the 
method  by  which  these  are  brought  about,  leads  to  another 
subdivision  of  both*  They  may  alter  the  amount  of  irri- 
tability, by  acting  either  on  the  composition  (in  the  che- 
mical sense)  or  on  the  structure.  As  agents,  it  is  not  ne- 
cessary that  they  should  always  effect  chemical  changes. 
Indeed,  by  doing  so  they  very  frequently  prove  injurious. 
The  influence  of  such  substances  as  do  not  sensibly  change 
the  composition  of  animated  matter,  is  extremely  obscure. 
Many  have  accounted  for  it,  by  supposing,  that  physical 
properties  were  displayed  by  the  constituting  particles ; 
hence  arose  the  terms  sharp,  dull,  or  rough  taste.  When 
we  consider,  that  every  body  has  a  peculiar  taste,  no  mat- 
ter what  its  composition  may  be,  and  that  the  effect  of 
tasting  does  not  seem  to  alter  such  chemical  composition, 
we  might  be  lead  to  suppose,  that  such  properties  depend 
upon  some  configuration  characterising  the  smallest  sensi- 
ble particles.  But  this  explanation  is,  at  present,  generally 
abandoned,  for  several  reasons.  Either  the  properties  of 
astringents  or  antispasmodics  must  be  in  opposition  to 
those  which  we  should  expect  to  follow  from  the  above 
explanation.  If  it  be  supposed  that  atomic  figure  can 
contract  the  irritable  fibre,  then  it  will  be  hardly  possible 
to  suppose  that  the  same  can  produce  a  relaxation.  We 
know,  moreover,  that  such  properties  result  from  the  che- 
mical composition,  and  that  the  body  possessed  of  them 
never  loses  them  by  any  mechanical  change.  Dr.  Park* 
observes,  that  "  the  various  kinds  and  degrees  of  sensa- 
tion which  arise  from  the  application  of  different  substances 
to  our  organs  may  be  referred  to  their  perculiar  modes  of 

*  Oft  the  Laws  of  Sensation,  Journal  of  Sciences  and  Arts,  No.  2. 


69 

action  ;  and,  accordingly,  they  are  as  various  as  the  nature 
of  the  substances."     This  gentleman  considers,  that  sen- 
sations are  produced  by  chemical  agents,  and  remarks, 
that  they  "  are  more  durable  in  their  impression,  as  they 
are  dissolved  in  the  fluids  on  the  sentient  surface,  and  re- 
quire more  time  for  the  changes  they  produce,  to  be  again 
obliterated  ;  and,  accordingly,  until  this  has  been  effected, 
the  organ  may  be  considered  as  having  its  susceptibility  for 
that  particular  impression  partially  suspended.     Or,  the 
substances  applied,  no  longer  producing  the  same  changes, 
no  longer  excites  the  same  sensation.     Thus,  substances 
kept  long  applied  to  our  organs  of  taste,  lose  their  power 
of  exciting  sensible  impressions  ;  as,  wine,  long  held  in  the 
mouth,  loses  the  flavour  peculiar  to  it,  and  if  several  kinds 
of  wine  be  tasted  in  quick  succession,  it  soon  becomes 
difficult  or  impossible  to  distinguish  them."     I  confess, 
when  these  effects  are  confined  to  a  short  space  of  time,  it 
is  impossible  to  perceive  any  thing  sufficiently  definite  to 
be   considered  chemical ;  but,  by  extending  the  review, 
there  seems  reason  for  supporting  the  opinion.     Nerves 
are  so  extremely  irritable,  that  the  most  limited  and  eva- 
nescent changes   of  structure  may  cause  sensation.     We 
know,  for  instance,  that  alcohol  has  the  property  of  coag- 
ulating albumen  in  the  animal  fluids,  by  uniting  to  the  al- 
kali which  renders  it  soluble.*     This  is  a  perfect  decom- 
position. When  flesh,  or  almost  any  animal  solid,  is  steeped 
in  alcohol,  the  albumen  coagulates,  and  forms  those  flakes 
which  render  the  fluid  turbid,  and  turns  the  whole  sub* 
stance,  after  some  time,  into  a  white  mass.     Now,  it  can 
readily  be  supposed,  that  such  a  change  which  subtracts 
both  the  alkali  and  albumen  from  the  substance  of  an  ir~ 

*  Brande's  Paper,  Phil,  Trans,  for  1809 


70 

ritable  nerve,  will,  at  its  commencement,  be  able  to  excite 
sensation.  All  the  alteratives  need  not  act  precisely  by 
this  decomposition ;  but,  the  instance  will  show,  that  they 
may  occasion  changes  capable  of  altering  the  extent  of  ir- 
ritability. Besides,  we  should  recollect,  that  such  sub- 
stances, by  acting  only  on  a  single  constituent,  may  prove 
very  effectual  without  our  being  able  to  perceive  the  least 
evidence.  Escharotics  are  known  to  destroy  nearly  the 
whole  texture,  as  well  as  composition,  and,  therefore,  we 
feel  less  hesitation  in  asserting  that  the  change  is  chemical. 
Many  of  these  substances  produce  similar  effects  on  the 
dead  and  living  matter  ;  and,  in  such  cases,  we  have  a  di- 
rect proof  of  their  nature.  Astringents  and  antiseptics 
are  of  this  kind.  The  agency  of  the  first  is  not  distinctly 
understood ;  but  we  know  that  it  does  not  depend  upon 
vitality,  since  the  same  takes  place  with  the  dead  fibre. 
Antiseptics,  on  the  other  hand,  must  act  chemically,  during 
life,  on  the  putrid  portion,  in  order  to  change  its  fetid 
smell,  and  therefore  we  may  extend  its  power  over  the 
others  which  are  nearly  in  the  same  state  ;  particularly 
since  we  find,  that  it  checks  or  destroys  their  tendency. 
Even  light,  which  is  a  stimulus  to  the  optic  nerve,  and 
which  is  known  to  convey  with  itself,  through  the  dense 
texture  of  glass  prism,  its  caloric  and  electricity,  may, 
when  it  enters  the  eye,  occasion  a  tendency  to  decomposi- 
tion, or  its  incipient  form.  Herschel,  in  making  his  obser- 
vations on  the  sun,  found  that  the  irritation  proceeded  from 
the  red  rays,  which  are  known  to  produce  heat  in  the  great- 
est degree ;  and  the  experiments  of  Mr.  Brande  (before 
noticed)  show,  that  a  very  small  power  of  electricity  is 
capable  of  affecting  albumen.  We  need  not  suppose  that 
such  incipient  changes  would  be  inconsistent  with  the  per- 
manent character  of  irritability ;  the  same  power  which 


71 

removes  the  nervous  matter  after  its  inevitable  and  inces- 
sant waste,  without  our  being  conscious  of  the  change, 
can  provide  for  both  cases.  When  we  consider  the  struc- 
ture of  a  nerve,  we  will  be  aware  of  the  number  of  varia- 
tions to  which  it  is  liable.  The  true  medullary  filaments 
are  surrounded  by  a  vascular  texture  which  follows  closely 
in  contact,  through  all  their  irregularity,  and  is  replete 
with  blood  vessels  analogous  to  the  pia  mater,  then  this  is 
cased  within  two  membranous  coats  exteriorly,  it  is  evi- 
dent, that  whatever  substance  causes  these  membranes  to 
contract,  will  diminish  the  circulation  of  blood  through 
the  nerve;  for  whether  the  medullary  matter  is  in  mass, 
and  incapable  of  contraction,  or  as  Mr.  J.  Bell*  supposed, 
in  zig-zag  filaments,  or,  as  has  lately  appeared,  in  globules, 
still  compression  or  elongation  of  the  whole  nerve  must 
shorten  its  diameter,  and  they  crowd  the  blood  vessels. 
Now,  as  Mr.  Bell  remarks,  "  pressure  by  impeding  the 
circulation  of  the  blood  in  these  vessels,  soon  effects  the 
sensibility  of  the  nerve ;  for,  however  the  function  of  the 
nerve  may  directly  result  from  its  organization,  yet  the  life 
and  vital  energy  is  received  from  the  blood  in  the  circula- 
tion through  it,  and  cannot  long  continue  if  that  blood  be 
interrupted  in  its  course."  Such  a  substance  as  has  the 
least  power  to  occasion  membranous  contraction,  will,, 
therefore,  have  a  tendency  to  lessen  sensibility,  or  in  other 
words,  to  act  as  a  sedative  ;  though  before  such  contraction 
takes  place,  its  presence  may  stimulate  or  increase  sensa- 
tion. Such  seems  the  nature  of  cold  applications,  and, 
perhaps,  such  sedatives  as  opium,  which  have  been  sup- 
posed in  the  first  instance  to  stimulate.  When  we  im- 
merse a  hand  in  very  cold  water,  at  first  the  sensation 

*  Anat. vol.2. 


72 

amounts  to  pain,  but  after  a  while  this  feeling  completely 
subsides,  or  is  at  least  lessened  very  nearly  to  that  extent ; 
yet  this  is  not  owing  to  the  subtraction  of  caloric,  for  if 
the  other  hand  be  immersed  in  water  of  the  same  tempera- 
ture as  the  first  at  the  time  sensation  ceased,  we  will  again 
be  effected  with  a  feeling  of  coldness.  Cold  air  contracts 
the  skin  when  it  occasions  numbness,  and  therefore  may 
effect  the  membranous  coats  of  nerves  in  the  same  way. 
But  it  is  useless  to  be  throwing  away  even  conjectures  ; 
the  subject  is  certainly  a  very  unsatisfactory  one,  and  the 
names  by  which  we  indicate  the  bodies  under  considera- 
tion may  be  the  least  likely  to  throw  light  on  their  true 
nature.  If  relaxation  of  habit  leads  to  an  excess  of  sen- 
sibility, then  astringents,  producing  an  opposite  action, 
may  appear  to  have  some  claims  for  the  character  of  a  se- 
dative. There  is  reason  to  suppose  that  the  irritability, 
or,  as  it  is  generally  called,  sensibility  of  a  nerve  is  inti- 
mately connected  with  the  degree  of  circulation  through 
its  substance ;  yet  the  principle  upon  which  its  existence, 
as  well  as  transmission  depends,  is  so  completely  obscure 
as  to  warrant  our  being  satisfied  with  the  knowledge  of  the 
mere  fact.  I  shall,  therefore,  pass  over  all  these  substances 
which,  acting  as  alteratives,  either  to  stimulate  or  allay 
the  irritable  fibre.  It  is  sufficient  to  remark,  that  if  these 
effects  do  not  depend  upon  chemical  action,  they  certainly 
do  upon  qualities  immediately  and  exclusively  resulting 
from  the  chemical  composition  of  bodies. 

The  next  subject  to  be  considered  is  the  formation  of 
animated  matter. 


73 

THIRD  DIVISION. 

PRODUCTION  OF  ANIMATED  MATTER. 
SANGUIFICATION* 

When  we  consider  the  complex  structure  of  the  living 
body,  as  well  as  the  routine  of  motions  constituting  its 
functions,  we  cannot  be  surprised  at  its  continual  decay. 
Admonished  by  appetite,  all  animals  endowed  with  the 
power  of  locomotion  seek  nourishment,  which  by  an 
operation  of  constitutional  changes,  obtains  the  power  of 
vitality,  and  takes  the  place  of  parts  no  longer  fit  for  vital 
functions.  Necessity  does  not  always  however  dictate 
hunger  or  thirst  ;  like  sleep  these  seem  to  follow  some 
laws  of  muscular  motion.  Man  generally  feels  his  peri- 
odical return  of  appetite  every  three  or  four  hours ;  (ex- 
cluding the  time  of  sleep,  where  there  is  little  or  no  active 
sensation  •,)  this  is  the  term  occupied  by  the  gastric  opera- 
tion, and  certainly  does  not  imply  any  corporeal  necessity, 
since  we  know  that  a  fresh  supply  has  passed  on  to 
minister  to  its  wants.  But  it  shows,  beside  the  force  of 
habit,  that  incessant  support  is  requisite  for  our  consump- 
tive fabric ;  all  its  laws  are  selfish  as  well  as  imperious. 
Whatever  may  be  the  form  of  habit,  we  find  that  the  effect 
for  which  it  is  intended,  always  is  more  perfect  when  it 
occurs  with  regularity.  Hence  the  uniform  return  of  ap- 
petite always  tends  to  give  better  sustenance  than  when 
more  nutricious  food  is  taken  at  short  and  irregular  peri- 
ods. In  the  animal  functions  there  are  two  principal 
causes  of  destruction — motion  and  chemical  affinity.  The 
first  is  always  augmented  by  health  and  muscular  exercise, 

10 


74 

and  gives  rise  to  the  necessity  of  more  food  at  one  time 
than  another ;  chemical  affinity,  on  the  contrary,  is  gene- 
rally speaking  a  permanent  cause,  since  the  matter,  which 
always  regulates  its  extent,  is  similar  from  one  period  to 
another.  Plants  have  no  locomotion ;  so  that  they  require 
a  less  amount  of  food,  as  well  as  a  more  uniform  supply. 
Assimilation  with  them  is  nearly  one  uninterrupted  pro- 
cess, until  circulation  ceases  in  the  autumn. 

In  the  following  remarks  I  shall  confine  myself  to  the 
assimilating  operations  of  mankind  chiefly ;  and  shall  di- 
vide the  subject  into  the  formation  of  blood  and  the  forma- 
tion of  the  animated  structure. 


DIGESTION. 

As  all  the  corporeal  structure  proceeds  from  the  blood, 
we  cannot  conceive  the  long  continuance  of  life  without 
this  fluid,  or  something  analogous  to  it.  Plants  have  a 
sap  which  is  capable  of  furnishing  all  the  solid  parts 
during  summer;  and  at  the  opening  of  spring  (during 
which  time  it  is  little  else  than  waterj  it  meets  with  nu- 
triment deposited  in  the  autumn,  so  as  to  become  enriched 
early  in  its  ascension.  Animals  which  are  called  cold 
blooded,  have  this  fluid  with  all  its  qualities  except  colour. 
In  short,  we  find  its  importance  manifested  in  every  form 
and  stage  of  life. 

The  source  of  blood  in  the  embryo  is  very  little  under- 
stood. But  the  most  probable  opinion  seems  to  be  that 
there  is  no  continuity  of  circulation  from  the  maternal 
vessels.*  We  see  this  fact  illustrated  in  eggs  and  seeds. 
The  chick  must  have  its  system  independent  of  the  hen  ; 
consequently,  we   must  suppose  that  it  fabricates  its  own 

*  Dr.  Chapman  on  Foetal  Circulation. 


75 

blood ;  the  same,  therefore,  may  take  place  in  the  uterine 
embryo.  How  this  is  effected  leads  to  a  very  obscure  but 
interesting  inquiry.  In  the  chick  the  blood  is  observed 
long  before  the  solid  structure,  and  therefore  can  hardly 
be  supposed  to  have  its  origin  from  any  extent  of  organic 
functions.  We  certainly  form  an  overrated  opinion  of 
the  sanguiferous  process  when  we  confine  our  views  of  it 
to  that  performed  by  the  adult.  Even  in  the  foetal  state 
we  must  cut  off  digestion  and  respiration,  and  in  the  early 
stages  of  existence  the  agency  of  vascular  connection. 
How  much  less  reason,  then,  is  there  for  supposing  a  vital 
origin  of  blood  at  the  time  when  it  is  confined  to  the 
punctum  saliens  or  irritated  speck  in  the  yolk  of  a  hen's 
egg.  If  on  the  other  hand  we  consider  the  materials  as 
well  as  the  vessels  of  a  limited  circulation,  as  being  fur- 
nished by  the  mother,  then  the  blood  may  originate  from 
the  external  application  of  chemical  agents,  as  heat,  light, 
&c. ;  influenced  by  these,  the  male  semen  may  also  com- 
bine in  the  formation  of  blood.  It  is  as  rational  to  sup- 
pose that  the  embryo  should  be  irritable  as  any  other  part 
of  the  female  body  which  results  from  assimilated  nutri- 
ment. But  I  shall  abandon  a  subject  which  is  so  mani- 
festly conjectural,  and  proceed  to  notice  the  process  by 
which  blood  is  formed  in  the  adult  system,  and  which  will 
be  found  to  give  strong  evidence  of  having  a  chemical 
origin.  The  food  is  masticated  in  the  mouth,  mixed  with 
the  saliva,  and  transferred,  by  swallowing,  into  the  sto- 
mach ;  here  it  undergoes  changes  of  composition  and  be- 
comes chyme.  This  chyme  passes  through  the  stomach 
into  the  duodenum,  where  it  meets  with  the  bile  and  pan- 
creatic juice,  and  by  their  chemical  action  becomes  chyle 
and  excrement.  As  these  substances  proceed  through  the  in- 
testines they  pass  by  a  system  of  absorbents,  called  lacte- 


76 

als,  which  gradually  take  off  the  chyle,  while  the  excre- 
ment, unfit  for  nutriment  from  the  beginning,  or  rendered 
so  in  consequence  of  the  changes  of  digestion,  continues 
to  proceed  through  the  intestines,  and  is  finally  evacuated. 
The  lacteals,  by  their  ramifications,  convey  the  chyle  into 
the  common  reservoir  of  all  absorbents,  called  the  thoracic 
duct ;  this  duct  opens  (in  man)  into  the  angle  formed  by 
the  union  of  the  left  subclavian  and  jugular  veins;  and 
thus  the  chyle  enters  the  blood.  It  is  then  carried  by  the 
circulation  to  the  lungs,  where  it  meets  with  changes 
which  convert  it  into  red,  and,  apparently,  perfect  blood. 
From  this  outline  we  perceive  three  important  changes  ; 
namely,  from  food  to  chyme,  from  chyme  to  chyle  and  ex- 
crement, and  from  chyle  to  blood.  These  are  certainly 
the  leading  ones ;  but  there  are  various  others  which  are 
not  so  notable.  We  shall  now  notice  the  foregoing  more 
particularly. 

It  has  been  contended  by  many  physiologists,  that 
digestion  begins  in  the  mouth.  In  some  animals,  whose 
appetite  seems  too  great  for  the  capacity  of  their  sto- 
mach, we  find  that  the  portions  which  they  swallow 
(but  which  are  unable  to  enter  lower  than  the  bottom 
of  the  oesophagus)  become  digested ;  it  is  probable  that 
the  saliva  then  performs  the  principal  operation,  since  it  pos- 
sesses so  strong  an  affinity  for  oxygen  as  to  become  charged 
with  it  before  it  mixes  with  the  food.  But  whether  this 
opinion  be  correct  matters  very  little  ;  we  know  it  acts  as 
a  solvent,  and  all  changes  which  it  could  produce  previous 
to  entering  the  stomach  must  be  very  limited.  The  quan- 
tity of  saliva  secreted  during  the  ordinary  meal  of  a 
healthy  man  has  been  estimated  at  six  ounces. 

It  has  been  concluded,  from  the  experiments  of  Ste- 
vens, Reaumur,  Spallanzani,  Scopoli,  Brugnatelli,  Cari- 
mini,  &c,  that  the  formation  of  chyme  is  brought  about  by 


77 

the  action  of  a  particular  liquid  secreted  by  the  stomach, 
and  therefore  called  the  gastric  juice.  It  seems  that  this 
operation  depends  upon  a  fluid ;  for  when  food  is  shut  up 
close  in  balls,  and  swallowed,  no  important  change  takes 
place ;  but  when  these  balls  have  holes,  the  food  becomes 
chyme.  The  process  terminates  in  three  or  four  hours. 
The  case  of  the  woman  in  the  clinical  ward  of  La  Cbarite, 
and  who  had  a  fistulous  opening  through  her  stomach, 
illustrates  the  regularity  of  this  period.  In  common  de- 
scription it  has  been  said,  that  the  gastric  juice  converts 
all  substances  into  chyme,  and  that  this  chyme  is  a  homo- 
genous substance.  We  are  to  consider  that  such  a  defini- 
tion of  the  power  peculiar  to  gastric  juice,  is  far  too  vague 
and  extensive. 

When  the  usual  food  has  been  suddenly  laid  aside  for 
other  of  a  different  kind,  we  know  that  bad  digestion  often 
takes  place.  Dr.  Adam's  experiments  go  to  prove  that 
the  gastric  juice  is  always  the  same;*  and  therefore  we 
may  consider  the  deficiency  to  arise  from  the  properties 
alone.  We  know,  further,  that  the  husks  of  grain,  woody 
fibres,  and  a  thousand  other  substances  in  food,  never  be- 
come chyme,  but  exist  as  mixtures.  This  fact  shows,  that 
chyme  is  not  a  homogenous  mass  ;  but  that  it  is  made  up 
by  a  compound  resulting  from  the  decomposition  of  sub- 
stances which  undergo  changes  readily,  as  well  as  of  such 
other  parts  whose  texture  and  composition  are  too  power- 
fully constituted.  Richerand  justly  remarks,  that  a  sub- 
stance to  be  fit  for  our  nourishment  should  be  capable  of 
decomposition  and  fermentation  ;  or,  in  other  words,  ca- 
pable of  undergoing  an  inward  and  spontaneous  change, 

*  On  Morbid  Poisons. 


78 

so  that  its  elements  and  relations  may  be  altered.*     This 
necessity  entitles  us  to  consider  that  digestion  is  of  a  che- 
mical nature.     Where  would  be   the  necessity  of  this  ten- 
dency to  chemical  changes,  if  they  were  to  be  opposed  by 
the  vital  influence  ?     If  the  chyme  were  always  to  be  of  a 
■similar  composition,  it  would  not  be  in  opposition  to  the 
opinion.       The    ultimate  constituents  of  all  animal  food 
are  always  the  same,   and  but  three   or  four  in  number : 
carbon,  hydrogen,  nitrogen  and  oxygen  ;  when  of  a  vege- 
table nature,  the  only  difference  will  be  in  the  absence  of 
nitrogen.     This  is  not  all  :  the  proximate  principles  of  food 
resemble  each  other  so  much  that  an  analysis  can,  in  some 
instances,  scarcely   make    out  the   difference  ;  and  those 
which  are  entirely  without  this  general  resemblance,  pass 
off  to  constitute  the  faces.     Thus,  a  dog  cannot  digest  the 
whole  bone  ;  his  gastric  power  cannot  assimilate  the  phos- 
phate of  lime  which  differs  from  the  gelatine  in  its  che- 
mical constituents,  and  not  in  texture,   since  mastication 
and  the  muscular  motion  of  his  stomach  reduce  both  to  an 
impalpable  consistence.     This  process  gives   the  appear- 
ance  of  assimilation  to   the   whole  mass :  but  when  the 
gelatine,  which  is  the  truly  digested  constituent,  becomes 
absorbed  by  the  lacteals,  we  find  the  earthy  salt  unaltered, 
and  constituting  the  excrement  called  album  grcecum.     I 
shall  pass   over  the  gastric  juice   itself,  since  all   the   me- 
thods hitherto  made  use  of  to  procure   it  are  not  only  ob- 
jectionable themselves,  but  they  have  led  to  unsettled  dis- 
putes   about  its   properties.     The    resemblance    that  the 
chyme  bears  to  a  homogenous  substance,  and   the  facility 
with  which  all  variety  of  food  enters  into  such  a  constitu- 
tion, have  led  physiologysts,  in   general,  to  deny  that  di* 

*  Phvsiolosrv. 


■79 

gestion  is  a  chemical  process  ;  it  shall,  therefore,  be  my 
present  object,  to  examine  the  solidity  of  this  opinion. 

In  the  first  place,  where  shall  we  look  for  limited  vital 
influence,  if  not  in  the  canals  and  cavities  of  the  body  ?  Is 
it  not  absurd  even  to  suppose  any  ?  As  I  have  before  re- 
marked, this  property  depends  upon  matter,  and  no  reason 
should  induce  us  to  suppose  that  it  may  exist  where  there 
is  none.  It  follows,  unequivocally,  that  where  inanimate 
substances  of  a  complex  nature  fill  up,  or  are  passing 
through  such  spaces,  that  their  tendencies  to  decomposi- 
tion will  be  as  strong  as  any  where  else  in  nature  under 
similar  chemical  advantages.  The  true  vital  economy  is, 
therefore,  in  taking  advantage  of  such  tendency,  by  fur- 
nishing chemical  agents  which,  by  their  affinity,  shall  give 
rise  to  the  compounds  observable  throughout  the  body. 
Of  such  a  nature  seem  the  gastric  and  pancreatic  juices, 
the  bile,  and  a  number  of  others. 

The  most  inconceivable  distinctions  have  been  adopted 
to  make  the  principles  of  life  as  little  understood  as  possi- 
ble. The  gastric  juice  has  been  endowed  with  a  vital 
influence  5*  but  what  can  be  more  absurd,  when  we  re- 
flect, that  this  fluid  while  separated  in  the  stomach  and 
mixed  with  the  food,  must  also  be  supposed  to  have  in- 
telligence of  what  is  good  or  what  is  bad  for  the  body  at 
large  ?  It  is  ridiculous  to  think  of  such  an  agent ;  the  gas- 
tric juice  must  produce  its  effect,  as  all  other  substances 
do,  by  chemical  or  physical  qualities  in  general.  Surely 
the  vital  functions  are  wonderful  enough  by  furnishing  this 
fluid,  rather  than  any  other  ineffectual  one,  without  making 
all  its  agents  conjurors.  But  it  is  begging  the  question, 
when  no  proof  can  be  offered.  Have  we  not  abundant 
proof,  that  the  vital  power  is  nothing  when  unconnected 

*  J.  Bell  Anat.  vol.  3.  page  214. 


80 

with  the  general  system  ?  There  is  not  a  single  part  of  the 
body,  even  the  most  highly  endowed,  which  can  when  un- 
connected, either  communicate  the  living  power  to  an  in- 
animate body  in  contact,  or  withstand  by  its  own  strength 
of  vitality  the  tendency  to  decomposition.     How  then  can 
we  consistently  suppose,  that  the  gastric  juice,  which  is 
sent  from  the  living  texture,  can  alone  possess  the  power 
of  making  the  food  resist  chemical   changes,  or  of  ob- 
taining, without  such  changes,  the   vital   property  ?    We 
might  as  well  maintain  that   the  bile,  pancreatic  juice, 
and  other  agents  for  decomposition,  operated  by  inherent 
vitality.     The   distinction  is  indeed,  since  the  most  im- 
portant change   seems   to    be   effected   by   these   fluids. 
On  general  principles,  there  should  be  as  great  an  anti- 
chemical  vitality  in  the  intestines   and  bladder,  as  in  the 
stomach ;  but  such  an  opinion  would  be  contradicted  by 
the  most  superficial  observation.     Mr.  John  Bell,  because 
he  was  informed  that  a  cow  can  digest  her  secundines  or 
membranes,  gives  up  his  faith  in  the  chemical  agency  of 
the  gastric  juice  :  "  This  throws  us   back,"  he  remarks, 
"  from  the  simple  idea  which  we  should  be  apt  to  entertain 
of  the  nature  of  the  change  produced  by  digestion,  viz. 
that  it  is  chemical.     For  we  see  that  the  nature  of  the 
solvent  thrown  out  from  the  stomach,  and  its  chemical 
properties,  may  be  changed  by  an  alteration  in  the  action 
of  the  coats  of  the  stomach."     It  remains,  however,  to  be 
proved  that  the  nature  of  the  gastric  juice  is  changed ; 
Dr.  Adam's  experiments  show  the  contrary.     And  even 
if  such  were  the  case,  it  would  only  prove,  what  is  already 
well  known,  that  one  body  acts  with  more  chemical  ener- 
gy than  another.    But  surely  we  cannot  overlook  the  fact, 
that  the  gastric  juice  is  emitted,  like  the  saliva  and  other 
secretions,  by  an  action  of  the  solid  texture.     There  is 


81 

nothing  more  strange  in  the  gastric  fluid  being  thrown  into 
the  stomach  more  profusely  by  the  presence  of  one  kind 
of  food  than  another,  than  that  the  saliva  should  be  secre- 
ted more   plentifully  by  savoury  meats  than  by  a  chip  of 
wood.  Until  we  are  better  acquainted  with  the  peculiarity 
of  stimuli,  we  cannot  say  that  such  is  not  the  case,  when 
the  usual  diet  has  been  changed.     But  after  all,  is  the  di- 
gestion of  meat  by  a  cow  or  horse    stranger  than  that  by 
man,  the  dog  or  cat  ?    Habit  makes  the  same  substance  be 
secreted  more  profusely  at  one  time  than  another,  and 
the  irritability  of  the  organ  itself  is   always    intimately 
concerned ;  since  less  nutritious  food  may  become  suited 
to  the  stomach,  and  its  bulk  as  well  as  indigestible  con- 
stituents even  promote  the  operation.     By  this  principle 
gramnivorous  animals  may  be  brought  to  live  on  animal 
food  ;  and  after  being  accustomed  to  this  their  stomachs 
will  become  incapable  of  digesting  vegetables,  and  vice 
versa  ;  even  man  whose  power  seems  most  general  from 
habit,  may  by  living  long  on  vegetable  food  be  rendered 
unfit  for  the  digestion  of  flesh.    I  am  far  from  maintaining 
that  this    process  is  independent  of  the  vital  influence. 
Whatever  may  be  the  nature  of  such  an  existence,  whether 
really  dependent  on  physical  properties  or  not,  we  must 
still  consider  its  phenomena  as  vital.     The  object  in  view 
is  to  show  that  laws  which  have  belonged  to  matter  since 
creation  are  not  destroyed  by  life  ;  and  that  the  nature  of 
our  conformation  directs  them  by  agents  which  they  would 
obey  any  where   else;  just  as  we  see  a  river  still  flowing 
through  all  its   natural  and  artificial  embankments.     We 
must  be  aware,  that  even  in  the  midst  of  the  most  vital 
substance,  decomposition  can  take  place  from  the  presence 
of  a  chemical  agent ;  no  one  surely  can  pretend  that  it  is 
the  vitality  of  that  part  itself  which  makes  amends  for 

11 


82 

those  changes.  The  connexions  with  hlood  vessels,  nerves. 
&c.  accomplish  this;  principally  from  being  themselves 
irritated  by  the  injury.  It  is  totally  unsupported  by  ana- 
logy to  give  this  multiplied  power  to  the  gastric  juice, 
even  though  of  an  irritable  nature ;  it  is  totally  devested 
of  connecting  organs,  as  nerves,  &c.  Much  less  can  we 
diffuse  it  through  cavities ;  particularly  when  matter  with 
the  strongest  tendency  to  decomposition,  is  passing  through 
them ;  and  some  of  which,  as  the  intestines,  are  found 
not  to  be  able  to  prevent  the  usual  chemical  changes  of 
putrefaction,  when  there  are  no  substances  furnished  with 
the  power  of  causing  a  new  play  of  affinities. 

I  shall  now  notice  some  further  chemical  parts  of  the 
process.  The  gastric  juice  is  said  to  be  antiseptic,  and 
this  has  been  considered  by  many  as  a  proof  of  its  vital 
agency.  There  is  not,,  however,  a  single  one  of  its  cha- 
racters so  decidedly  chemical  as  this ;  besides,  it  is  no 
property  of  life  that  one  isolated  substance  should  protect 
another  and  prevent  decay.  The  analogy  is  probably 
drawn  from  an  injured  limb  recovering  its  strength ;  but, 
again,  it  must  be  repeated,  that  the  limb  does  nothing  but 
receive  the  changes.  Its  irritable  structure  prompts  the 
action  which  propels  the  new  supply ;  but  cannot  alone 
protect  the  limb.  So  it  is  with  every  detached  produc- 
tion of  the  body,  though  endowed  with  the  most  delicate 
irritability^  unless  possessed  also  of  an  independent  circu- 
lating system,  its  operation  of  defending  itself,  or  any  other 
body  in  contact,  by  that  property,  is  no  stronger  than  that 
of  inanimate  matter. 

The  operation  in  the  stomach  of  rabbits,,  as  stated  by  Dr. 
Wilson  Philip,*  shows,  that  digestion  takes  place  on  the 

*  On  the  Vital  Functions 


83 

surface  of  the  food  where  it  lies  in  contact  with  the  sto- 
mach, which  is  the  source  of  the  gastric  fluid.  For  this 
purpose  we  see  the  utility  of  a  fact  stated  by  that  author, 
namely,  that  after  a  short  time,  these  surfaces  of  food 
change,  and  are  carried  by  muscular  motion  to  the  pyloric 
extremity,  until  the  central  portions  are  brought  in  contact 
with  the  stomach.  There  is  also  a  property  of  the  sto- 
mach, particularly  that  of  a  calf,  whereby  milk  and  the 
serum  of  blood  are  coagulated  immediately.*  This,  very 
probably,  acts  an  important  part  of  digestion ;  but,  if  so, 
it  must  be  by  its  chemical  properties  alone,  since  Dr. 
Young's  experiments  in  particular  show  that  the  opera- 
tion goes  on  as  well  out  of  the  body.  This  gentleman 
found  that  seven  grains  of  the  inner  coat  of  a  calf's  sto- 
mach, infused  in  water,  gave  a  liquid  which  coagulated 
more  than  a  hundred  ounces  of  milk ;  that  is  to  say,  more 
than  6,857  times  its  own  weight.!  Is  it,  therefore,  so  re- 
markable, that  with  such  an  agent  as  this,  the  food  should 
be  made  to  enter  into  other  chemical  compounds  than  those 
of  fermentation  or  putrefaction  ?  As  to  its  utility,  our  im- 
perfect knowledge  of  coagulation  prevents  a  decided  opi- 
nion ;  it  evidently  separates  the  albumen  of  food  with 
great  readiness,  and,  therefore,  may  be  the  means  em- 
ployed to  furnish  that  highly  important  material  to  the  sys- 
tem without  requiring  its  reformation.  It  is  to  be  remark- 
ed, however,  that  other  offices  would  have  to  combine ; 
and  there  is  no  experimental  foundation  for  the  opinion. 
It  need  not  now  be  urged  as  an  objection  to  the  chemical 
character  of  digestion,  that,  unless  in  disordered  health, 
there  is  no  complete  fermentation  or  putrefaction.  The 
very  phenomena  of  dyspepsia  show,  that  the  tendency  is 

*  Hunter's  Animal  Economy.  t  Thomson's  Chem.  vol.  iv. 


84 

never  extinct ;  and  facts  well  established  all  go  to  prove, 
that  the  nature  of  the  process  consists  not  only  in  a  series 
of  active  chemical  changes,  but  in  a  muscular  arrange- 
ment to  discharge  the  food  before  its  natural  tendencies, 
even  out  of  the  body,  could  be  developed.  After  under- 
going imposed  changes  in  the  stomach,  and  remaining  there 
only  for  the  short  space  of  three  or  four  hours,  it  is  evacu- 
ated into  the  duodenum,  there  immediately  to  undergo 
others.  Now,  where  I  would  ask  is  the  time  or  opportu- 
nity for  spontaneous  changes  ?  Nay,  beside  these  now  men- 
tioned, it  can  be  shown,  by  another  arrangement,  that  na- 
ture designs  that  they  should  occur  as  little  as  possible. 
Dr.  Philip*  states,  that  the  food  which  is  in  the  py loric  por- 
tion of  the  stomach  is  always  most  perfectly  digested,  and 
is  quite  dry  in  comparison  to  the  undigested  food  at  the 
cardiac  extremity,  which  is  mixed  with  a  large  proportion 
of  fluid.  What  more  obvious  deduction  can  we  draw  from 
this  singular  fact  than  that  the  pyloric  portion  of  food, 
since  it  has  undergone  all  the  imposed  changes  which 
should  occur  in  the  stomach,  is  rendered  comparatively 
dry,  in  order  to  diminish  its  lasting  tendency  to  spontaneous 
decomposition  ;  while,  on  the  other  hand,  that  at  the  car- 
diac portion  is  mixed  with  fluid  to  promote  more  rapidly 
the  action  of  the  gastric  juice,  &c.  1  shall  now,  in  a  ge- 
neral manner,  bring  to  view  the  circumstances  which  in- 
duce chemical  action  in  the  stomach ;  and  by  keeping  in 
view  the  foregoing  remarks,  we  will  be  enabled  to  con- 
clude correctly  as  to  their  nature. 

1st.  The  saliva  is  a  fluid  wiih  a  strong  affinity  for  oxy- 
gen ;  the  general  agency  of  solution  is  also  augmented  by 
the  gastric  juice.     The  importance  of  this  state  of  consis- 

*  Vital  Functions, 


85 

tency  has  led  to  the  axiom  "  corpora  non  agunt  nisi  sint 
soluta,"  and  its  truth  has  scarcely  met  with  a  contradic- 
tion. Our  conformation  bears  testimony  of  its  importance 
during  digestion.  Teeth,  or  something  analogous,  are  al- 
ways requisite  to  grind  down  the  food.  When  these  do 
not  perform  their  office,  the  ill  effects  are  manifest ;  very 
old  persons  without  teeth,  or  such  persons  who  eat  in 
haste,  or  bolt  their  food,  are  generally  troubled  with  indi- 
gestion. 

2d.  There  is  an  elevation  of  temperature  during  diges- 
tion. This  circumstance  conduces  to  chemical  action, 
whether  it  is  furnished  for  the  purpose,  or  exists  as  a  con- 
sequent. Cold-blooded  animals  are  known  to  digest  much 
slower  than  hot-blooded  ones  ;  and  Spa'lanzani  has  shown, 
that  the  gastric  juice5  at  a  temperature  below  seven  de- 
grees Reaumur,  or  about  48  degrees  Fahrenheit,  is  no  more 
effectual  in  softening  or  dissolving  food,  than  plain  water.* 
If  we  consider  this  elevation  of  temperature  as  a  conse- 
quent of  digestion,  then  there  will  be  more  reason  for 
supposing  that  true  chemical  changes  occasion  it. 

3d.  The  properties  of  such  food,  as  have  undergone 
perfect  digestion,  are  completely  changed,  both  as  to  taste, 
smeil,  and  colour.  These  changes  begin  so  soon  that  after 
the  food  has  remained  a  few  minutes  in  the  stomach,  they 
can  be  easily  noticed.  This  fact,  as  Speert  justly  re- 
marks, shows  that  chemical  action  is  the  first  to  take 
place  in  the  stomach,  since  no  other  power  could  have 
operated  in  so  short  a  *ime. 

4th.  The  digestion  generally  takes  place  best  in  such 
food  as  most  readily  undergoes  chemical  decomposition. 

5th.  The  gastric  juice  acts  on  the  stomach  itself  after 
life.     Mr.  Hunter  long  ago  noticed  this   fact  on  the  hu- 

*  Richerand's  Physiol.  t  On  the  Stomach. 


86 

man  stomach.  (Phil.  Trans,  for  1772.)  This  gentleman 
supposed  it  necessary  that  the  animal  should  be  in  health, 
immediate)}'  preceding  death,  in  order  that  the  secretion 
of  the  gastric  juice  may  be  natural,  and  capable  of  dis- 
solving the  dead  stomach;  but  Mr.  John  Bell  remarks, 
that  he  found  the  stomach  of  children,  who  had  died  after 
a  long  illness,  digested  by  the  secretion  of  the  stomach.* 
Dr.  Wilson  Philip  states  that  the  gastric  juice  of  rabbits 
can  so  completely  digest  its  own  stomach,  after  death,  as 
to  leave  no  trace  of  former  structure.  (Enquiry  into  the 
Vital  Functions.)  Now,  it  may  be  asked  why  the  gastric 
juice  does  not  produce  the  same  effect  during  life,  pro- 
vided its  agency  is  chemical  ?  To  this  it  ma)  be  answered, 
that  like  all  other  changes  in  the  living  body,  even  if  it 
does  take  place,  we  may  be  so  constituted  as  not  to  be 
aware  of  it.  But  the  best  reason  seems  to  be  that  the 
living  stomach  is  always  covered  with  its  peculiar  fluids, 
which  by  interposition  defend  the  living  structure,  and 
which  must  be  thrown  out  on  its  surface  by  ever}7  irritating 
material.  In  the  stomach  there  exists  an  abundance  of 
what  Mr.  Bell  calls  the  "  general  vascular  secretion" 
mixed  with  its  glandular  secretions  ;t  these  must  evidently 
be  decomposed  even  before  the  organization,  furnishing  the 
gastric  juice,  can  be  acted  upon  ;  and  during  life  such 
changes  are  prevented  from  extending  by  a  constant  ab- 
sorption and  fresh  secretion.  After  life,  this  vascular  se- 
cretion can  only  serve  as  a  protection  while  it  remains 
unaffected  ;  but  after  decomposition  takes  place  it  even 
acts  injuriously  by  the  absence  of  absorption.  The  pro- 
tecting effect  of  fluids,  which  apparently  for  this  purpose 
cover  the  smallest  fibres,  may  be  noticed  among  fishes  ; 
where  it  is  remarked  that  those  which  can  throw  out  on 

*  Anat.  vol.  3.  f  Anat.  vol.  3. 


87 

their  bodies  the  most  of  that  thick  mucous  fluid  which 
characterises  all  of  them,  more  or  less,  can  remain  long- 
est alive  when  exposed  to  the  action  of  the  air. 

Now,  does  it  not  seem  unreasonable  to  suppose  that  all 
these  chemical  agents  should  be  crowded  together  in  one 
process,  and  that  the  most  natural,  without  that  process 
being  chemical  ?  If  only  one  were  observable  we  might 
hesitate  ;  but  I  cannot  see  how  we  can  overlook  the  pre- 
sence of  so  many.  It  has  been  said  that  gases  should  re- 
sult from  chemical  changes  in  the  stomach.  This  un- 
doubtedly would  be  the  case  if  the  decomposition  de- 
pended upon  the  internal  action  of  the  nutritious  parti- 
cles; provided,  also,  they  remained  a  sufficient  time  under 
such  circumstances,  which  is  found  not  to  be  the  case.  It 
by  no  means  follows  that  the  same  result  should  take  place, 
where  the  decomposition  is  effected  by  one  agent,  as  the 
gastric  juice.  But  I  shall  show,  that  with  all  this  arrange- 
ment the  most  unequivocal  signs  of  spontaneous  de- 
composition do  actually  exist  in  a  limited  degree.  Drc 
Prout,  whose  authority  stands  high  on  this  subject,  ob- 
serves, that  "  a  gaseous  product  is  usually  evolved"  during 
the  action  of  the  gastric,  pancreatic,  and  biliary  fluids.* 
By  other  authorities  it  seems,  also,  that  the  gases  formed 
through  the  alimentary  canal  (including  the  stomach)  have 
a  fixed  ratio  and  relation  to  each  other.  "  From  the  ex- 
periments of  Magendie  and  Chevreul,  it  appears  that  the 
oxygen  gas  which  usually  exists  in  the  stomach  in  a  con- 
siderable proportion  when  compared  with  the  other  gasesr 
gradually  diminishes,  and  at  last  disappears  as  we  pro- 
ceed along  the  course  of  the  alimentary  canal;  while  at 
the  same  time  the  proportion  of  carbonic  acid  and  hydrogen 
gas  increases."!  The  following  gives  a  view  of  their  results. 

*  Ann.  Philos.  for  1819,  t  Thompson's  Chem.  book  5, 


88 


Oxyg.       Carb.  acid  )  Hydrog.  |   Nitrog.   |  Carb.  hyd. 


Stomach, 

Ccecuta, 

Rectum, 


11  00 

00  00 
00  00 


14  00 
12  50 
42  86 


3  55 

7  40 
0  00 


71  45 

67  58 
45  96 


00  00 
12  50 
11   18 


- 


100. 


In  the  small  and  large  intestines  these  gases  were  also 
found  to  exist  in  variable  and  considerable  quantities,  but 
with  less  regularity.  These  gentlemen  examined  the  bo- 
dies of  four  criminals  executed  in  Paris,  very  soon  after 
death.  Their  results  may  be  seen  more  particularly  in 
the  Ann.  de  Chim.  et  Phys.  ii.  292. 

We  learn  from  Dr.  Prout's  paper  on  sanguification,*  be- 
fore alluded  to,  that  the  chyme  itself  gives  no  traces  of  an 
albuminous  principle ;  (in  which  term  Dr.  Prout  in- 
cludes the  perfect  albumen,  fibrine  and  colouring  principle 
of  the  blood ;)  but  that  its  formation  takes  place  in  the 
duodenum,  and  some  distance  down  in  the  intestines.  The 
most  important  change  must,  therefore,  take  place  after 
the  chyme  leaves  the  stomach,  and  unites  to  the  bile  and 
pancreatic  juice.*  This  gentleman  is  of  opinion,  that  the 
blood  begins  to  be  formed  from  the  food,  in  all  its  parts, 
from  the  first  moment  of  its  entrance  into  the  duodenum. 

As  to  the  action  of  the  bile  and  pancreatic  juice,  little 
is  distinctly  known  except  their  importance  ;  though  even 
this  point  has  been  questioned.  Berzelius  has  shown  that 
the  bile  becomes  decomposed  by  its  union  with  the  chyme ; 
and  Dr.  Prout,  in  his  paper  on  sanguification,  states,  that 
he  always  found  that  the  acidity  of  the  chyme,  which  was 
almost  invariable,  became  neutralized  by  its  addition.  Now, 
these  facts  show  the  importance  of  bile  ;  notwithstanding 
the  remark,  that  when  the  ductus  communus  choledicus  is 
obstructed,  no  manifest  deficiency  of  chyle  is  observable. 
Probably  the  truth  would  not  be  so  favourable  were  the 
fact  better  established. 


Ann.  Philos.  for  1819. 


f  Thompson's  Chem.  book  v. 


89 

I  have  but  a  few  remarks  to  offer  on  the  chyle.     While 
in  the  intestines,  or  mouths  of  the  lacteals,  its  true  charac- 
ter is   hardly  perceptible  ;  it  undergoes  coagulation  very 
slowly  and  imperfectly,  and  does  not  assume  a  reddish  co- 
lour when  exposed  to  the  air.    Hence,  Dr.  Prout  supposes, 
that  it  then  contains  a  very  small  proportion  only  of  a 
principle  analogous  to  fibrine,  "  or  at  least  this  principle 
exists,  as  yet,  in  a  very  imperfect  state,  and  no  colouring 
matter."     When  the  chyle  is  found  in  the  thoracic  duct, 
(where  the  absorbents  empty  their  contents  from  the  body 
at  large,)  it  bears  a  close  resemblance  to  blood,  and  seems 
only  to  differ  in  its  colour.     To  a  certain  degree  it  also 
has  the  last  quality  ;  for  its  white  particles  become  pink- 
ish when  exposed  to  the  air.*     This  perfection  of  chyle, 
without  any  manifest  progress,  may  result  from  a  tendency 
to  inward  changes,  first  established  in  the  duodenum  and 
intestines.      The   absorption   by   lacteals   seems,  as  Dr. 
Prout  remarks,  to  be  merely  a  mechanical  process.     One 
of  the   most  singular  phenomena  that  occur  during  the 
process  of  vegetable  digestion,  is  the  formation  of  nitrogen. 
The  flesh  and  other  parts  of  an  animal  confined  altogether 
to  this  kind  of  food,  contains  nitrogen  gas  as  a  constituent, 
although  vegetables  are  almost  all  without  it.     This  is  very 
singular,  inasmuch  as  nitrogen  has  not  yet  been  decom- 
posed, while  no  doubt  can  be   entertained  but  that  it  oc- 
curs from  digestion.     Its  compound  nature  has  been  sus- 
pected, however,  by  several  chemists,  and  Mr.  Miers  pub- 
lished a  number  of  ingenious  experiments  in  order  to  show 
that  it  is  a  compound  of  oxygen  and  hydrogent     Berze- 
lius  maintained  that  it  is  not  a  simple  substance.  J     When 
we  consider  that  it  must  have  been  produced  by  the  pro- 

*  Prout.  t  Ann.  Philos.  iii.  and  iv.  %  Ann.  Philos.  U. 

12 


m 

cess  of  digestion,  we  will  form  a  better  opinion  of  its  na- 
ture by  suspecting  the  correctness  of  our  knowledge,  or  at 
least  the  deficiency  of  the  means  which  are  possessed  to 
detect  its  composition.  During  the  respiration  of  nearly 
pure  oxygen  gas,  a  portion  of  it  disappears,  and  an  equal 
bulk  of  nitrogen  appears  in  its  place.  The  substitution  is 
greatest  at  the  commencement,  and  amounts  at  an  average 
to  near  80  cubic  inches.  This  curious  fact  was  established 
by  Messrs.  Allen  and  Pepys,  whose  experiments  on  respi- 
ration were  conducted  on  a  very  large  scale.  Yet,  in  the 
ordinary  process,  no  nitrogen  seems  to  be  formed.  So, 
also,  when  a  mixture  of  79  hydrogen,  and  21  oxygen  gas, 
is  breathed,  nitrogen  appears  among  the  products.  The 
experiment  seems  to  confirm  Mr.  Miers's  idea  not  only  of 
the  compound  nature  of  nitrogen,  but  of  its  constituents. 
Indeed,  when  we  consider  how  instantaneously  carbon 
unites  to  oxygen  during  respiration,  we  will  be  less  sur- 
prised that  hydrogen  should  also  combine  with  oxygen, 
and  form  a  compound  not  to  be  imitated  easily  in  the  la- 
boratory. 

RESPIRATION. 

I  shall  finish  this  view  of  the  sanguiferous  process 
by  continuing  the  remarks  on  respiration.  It  is  re- 
markable that  this  process  so  universally  imperious 
upon  all  kinds  of  animals,  never  has  manifested  more 
than  two  offices ;  that  of  giving  colour  and  fibrine  to  the 
chyle,  and  that  of  subtracting  carbon  from  the  system.  I 
cannot  but  think,  that  the  extent  of  its  importance  is  highly 
undervalued.  All  the  labours  of  philosophers,  for  years 
past,  have  been  concentrated  in  the  few  gases  effected  by 
respiration ;  and  all   the  changes    produced  both  on  the 


91 

chyle  and  blood,  have  been  limited  to  the  subtraction  of 
carbon.  It  appears  to  me,  that  more  important  and  definite 
knowledge  would  arise  were  the  investigation  confined  to 
the  blood  itself,  than  to  the  external  characters  of  respira- 
tion; the  true  changes  must  exist  in  the  blood  of  the  pul- 
monary veins,  and  more  solid  information  might  accrue, 
by  comparing  this  with  the  blood  of  the  pulmonary  arte- 
riesj  which  is  replete  with  the  matter  about  to  be  changed. 
It  is  not  so  important  to  know,  that  carbon  is  given  off  as 
to  know  in  what  state  such  a  change  has  left  the  circula- 
ting materials.  We  have  yet  to  learn  why  it  is,  that  car- 
bon seems  in  such  profusion  and  waste,  whereas  the  oxy- 
gen, hydrogen,  and  nitrogen,  never  make  their  appear- 
ance as  separate  secretions.  The  supply  of  all  is  daily 
continued  from  the  nutriment ;  and  carbon  is  generally 
found  in  the  compound  secretions,  as  well  as  the  others. 
This  substance  must  result  chiefly  from  the  waste  of  all 
the  organic  texture,  (since  the  chyle  is  but  a  trifling  in- 
terference both  from  quantity  and  quality  ;)  what  then  be- 
comes of  the  other  constituents  ?  the  absorbents  which 
take  up  one  must  take  up  all,  if  the  decomposition  be 
effectual,  and  convey  them  into  the  circulation  ;  yet  here 
they  have  not  been  found  in  a  separate  state  ;  but  if  they 
form  soluble  combinations,  the  blood  seems  best  adapted 
to  display  them.  As  it  is,  respiration  consists  in  the  evolu- 
tion of  carbon,  and  in  the  negative  effect  of  giving  the  ve- 
nous blood  a  florid  colour,  (since  it  is  the  absence  of  car- 
bon which  seems  to  cause  this  phenomenon.)  During  this 
process  there  is  a  separation  of  moisture,  which  arises 
principally  from  the  substance  of  the  lungs ;  experiments 
show  that  little  or  none  of  the  atmospheric  oxygen  goes 
for  its  formation.  Crawford  has  also  determined  that 
venous  blood  has  less  specific  caloric  than  arterial  blood, 
in   the  proportion  of  8.9,.  to  10.3.  and  therefore,  the  la- 


92 

tent  caloric  of  the  former,  as  it  becomes  liberated  during 
respiration,  enters  into  union  with  the  arterial  blood,  as  fast 
as  it  is  formed,  and  thus  leaves  the  lungs  at  their  original 
temperature.  During  circulation,  the  arterial  blood  is 
gradually  converted  into  venous ;  consequently,  its  specific 
caloric  diminishes,  and  it  must  give  out  heat.  This  is  the 
reason  that  the  temperature  of  the  extremities  does  not 
diminish,  or  that  of  the  lungs  increase.  Dr.  Davy  has  since 
proved,  that  Crawford's  estimate  is  by  far  too  high  ;  since 
he  found  that  the  specific  caloric  of  arterial  blood  is  but 
0.913,  when  that  of  other  is  0.903.  Dr.  Crawford  also 
adopted  the  theory  of  Dr.  Black ;  by  supposing  that  a 
great  quantity  of  caloric  is  given  out  by  the  union  of  oxy- 
gen and  carbon,  which  he  considered  sufficient,  not  only 
to  carry  off  the  newly  formed  water  in  the  state  of  vapour, 
and  to  raise  considerably  the  temperature  of  the  air  re- 
spired, but  to  support  the  temperature  of  the  body.  This 
has  also  met  with  a  contradiction  from  the  examination  of 
Delaroche  and  Berard,  who  have  shown  that  the  specific 
caloric  of  oxygen  and  carbonic  acid  differ  much  less  than 
Crawford  supposed  ;  that  of  the  first  being  but  0.8848, 
when  the  last  is  0.828.  The  theory  of  Dr.  Crawford 
displays  unusual  elegance,  but  we  must  look  elesewhere 
than  on  respiration  to  discover  the  true  sources  of  animal 
heat.  Chemical  changes  no  doubt  contribute  largely,  but 
they  are  not  those  in  the  lungs.  Thus  then,  though  un- 
willingly, we  are  obliged  to  curtail  the  function  of  respi- 
ration to  its  power  of  subtracting  carbon.  Its  operation 
on  the  chyle  is  thus  described  by  Dr.  Thompson  ;*  "  It 
appears  from  the  most  accurate  observations  hitherto  made, 
that  neither  chyle  nor  lymph  contain  fibrine,  which  forms 
a  conspicuous  part  of  the  blood.  This  fibrine  is  employ- 
ed to  supply  the  waste  of  the  muscles,  the  most  active 

*  Chem.  books. 


93 

parts  of  the  body,  and  therefore  in  all  probability  requir- 
ing the  most  frequent  supply.  Nor  can  it  be  doubted  that 
it  is  employed  for  other  useful  purposes.  The  quantity  of 
fibrine  in  the  blood,  then,  must  be  constantly  diminishing, 
and  therefore,  new  fibrine  must  be  constantly  formed.  But 
the  only  substances  out  of  which  it  can  be  formed  are. 
the  chyle  and  lymph,  neither  of  which  contain  it.  There 
must,  therefore,  be  a  continual  decomposition  of  the  chyle 
and  lymph  going  on  in  the  blood  vessels,  and  a  continual 
new  formation  of  fibrine.  Other  substances  also,  may  be 
formed;  but  we  are  certain  this  must  be  formed  there,  be- 
cause it  does  not  exist  previously.  Now,  one  great  end  of 
respiration  must  undoubtedly  be  to  assist  this  decomposi- 
tion of  chyle,  and  complete  formation  of  blood.  In  what 
manner  the  chyle,  or  a  part  of  it,  is  converted  into  fibrine, 
it  is  impossible  to  say ;  we  are  not  sufficiently  acquainted 
with  the  subject  to  be  able  to  explain  the  process.  But 
we  can  see,  at  least,  that  carbon  must  be  abstracted  from 
that  part  of  the  chyle  which  is  to  be  converted  into  fibrine. 
Hence,  as  the  process  of  blood  making  advances,  there 
must  be  a  greater  and  greater  redundance  of  carbon  in 
the  liquid.  Unless  this  redundance  were  removed,  the 
process  could  not  go  on,  and  probably  the  whole  would 
run  into  putrefaction.  We  may  conclude,  then,  that  one 
great  use  of  respiration  is  to  abstract  this  carbon,  by  form- 
ing with  it  carbonic  acid.  How  this  is  performed,  indeed, 
it  is  impossible  at  present  to  explain;  but  the  fact  is  un- 
doubted." Messrs.  Allen  and  Pepys  have  shown,  by  their 
experiments,  that  the  body  of  a  healthy  full-sized  man, 
gives  off  daily,  by  respiration,  an  average  of  eleven  troy 
ounces  of  solid  carbon.  This  must  evidently  be  infinitely 
more  than  what  proceeds  from  chyle,  since  chyle  is  but 
an  exceedingly  small  proportion  of  the  food  eaten.     One 


94 

year  of  such  respiration  would  make  a  man  give  off 
from  his  lungs  near  335  pounds  troy  of  solid  carbon, 
a  weight  which  almost  equals  twice  the  body  itself. 
Dr.  Prout*  has  shown  that  the  carbon  they  evolved  is 
different  in  different  periods  of  the  day.  At  noon  it  is 
near  its  maximum,  and  at  its  minimum  about  midnight ;  and 
at  morning  twilight  it  begins  to  increase.  This  gentle- 
man also  found,  that  alcohol  and  all  fermented  liquors  di- 
minished the  proportion,  and  likewise  that  when  the  con- 
stitution is  affected  by  mercury  the  same  takes  place. 
Dr.  Fyfe  remarked  the  same  phenomena,  and  observed 
further,  that  a  course  of  nitric  acid  and  vegetable  diet 
produced  the  same  effect.!  Fishes  require  but  little  at- 
mospheric air  :  it  appears  that  a  man  consumes  fifty  thou- 
sand times  as  much  oxygen  gas  as  a  trench.  J  Yet  the 
presence  of  this  principle  is  equally  necessary  for  the  ex- 
istence of  both  and  for  all  other  animals.  These  are  the 
principle  facts  of  respiration ;  with  which  I  shall  close  this 
subject.  There  is  no  function  more  purely  chemical  as 
far  as  it  is  at  present  understood;  for  a  full  and  impartial 
detail  I  cannot  refer  to  a  better  work  than  that  of  Dr.  Bos- 
tock. 

FOURTH  DIVISION. 

ASSIMILATION. 

Before  entering  on  this  intricate  consideration,  it  will 
be  but  justice  to  remark,  that  speculation  constitutes  its 
great  features.  We  know  the  materials  and  the  product, 
but  know  little  positively  of  the  agents  proximately  con- 
cerned, or  of  their  connexion  during  the  progress  of  as- 
similation.    Wherever,  however,  experiments  appear,   I 

*  Ann.  Philos.  2.  and  4.       t  Ibid  4.       i  Thompson's  Chem.  book  §. 


95 

shall  give  them  place,  if  sufficiently  authentic,  no  matter 
what  opinion  they  may  contradict,  or  what  unpleasant 
conclusion  they  may  lead  to.  This  is  absolutely  neces- 
sary if  truth  is  at  all  to  be  regarded  upon  the  subject  of 
our  existence;  and  when  they  are  as  fairly  impeached  as 
they  have  been  established,  and  by  the  same  experimental 
method,  it  will  be  the  only  time  to  overlook  them  or 
throw  them  aside. 

COMPOSITION  AND  FIGURE. 

I  have  before  remarked,  that  the  blood  of  animals  and 
the  sap  of  vegetables  furnish  the  materials  for  assimila- 
tion. The  formation  of  these  fluids  should  also  be  in- 
cluded within  this  process  ;  but  I  have  already  noticed 
that  operation,  and  there  seems  naturally  to  be  a  distinc- 
tion. My  first  examination  will  be  of  the  blood  itself. 
When  the  blood  has  been  drawn  from  an  animal,  and  al- 
lowed to  stand,  it  coagulates,  and  by  this  process  be- 
comes divided  into  two  parts.  The  coagulum  itself  (which 
has  also  been  called  cruor,  because  it  alone  retains  the  red 
colour  peculiar  to  blood)  constitutes  one  part,  and  the 
other  consists  of  a  limpid  straw-coloured  fluid,  which  is 
called  serum.  Diseases,  and  a  variety  of  different  other 
circumstances  have  the  power  of  altering  the  proportion 
of  these  constituents ;  but  that  most  usual  is  about  one 
part  of  cruor  to  three  of  serum.*  Blood  by  the  same  pro- 
cess gives  out  vapour  with  a  peculiar  smell  as  well  as  some 
carbonic  acid  gas  which  was  formed  and  dissolved  previous 
to  coagulation.  This  spontaneous  decomposition  of  the 
blood  is  not  retarded  or  promoted  by  external  agents,  such 

*  Thomson's  Chera.  book  v. 


96 

as  air  or  its  absence,  temperature  or  dilution  with  water ; 
electricity  when  given  in  large  shocks  through  the  body 
has  been  said  to  prevent  the  coagulation  ;  such  is  also  the 
effect  of  violent  and  fatal  passions.*  The  cause  seems 
confined  to  the  blood  itself;  and  the  peculiarities  of  its 
operation  led  Mr.  Hunter  to  suppose  that  the  blood  has 
vital  properties:  Dr.  Gordon  has  rendered  it  probable 
that  heat  is  thus  evolved. t 

The  serum  is  found  to  contain  either  a  free  or  car- 
bonated alkali,  since  it  turns  the  syrup  of  violets  to  a  green 
colour.  Rouelle  and  Dr.  Marcet  determined  that  the  al- 
kali is  soda,  whereas  Dr,  Pearson  very  plausibly  considers 
the  alkali  in  the  animal  fluids  to  be  potassa.  It  is  proba- 
bly of  little  consequence  either  way,  as  both  have  the 
power  of  dissolving  albumen,  which  seems  their  most  ex- 
tensive use  in  the  animal  economy.  Serum  also  contains 
albumen  in  a  considerable  quantity,  also  a  very  large  pro- 
portion of  water.  Lactate  of  soda,  and  the  muriates  of 
soda  and  potassa  to  a  very  trifling  amount,  as  well  as  diffe- 
rent phospates.  Berzelius  is  of  opinion  that  phosphorus 
sulphur,  and  the  bases  of  lime  and  magnesia,  exist  as  con- 
stituents of  albumen,  and  are  only  produced  as  salts,  he. 
by  incineration. 

The  cruor,  when  carefully  washed  by  a  gentle  stream  of 
cold  water,  is  separated  into  a  white,  solid,  and  elastic  sub- 
stance, having  all  the  properties  of  Jibrine,  and  into  the 
colouring  matter  which  the  water  dissolves.  Berzelius  and 
Brande  have  shown  that  the  cruor  also  contains  albumen  ; 
but,  as  Dr.  Thomson  remarks,  it  is  impossible  to  separate 
the  serum  completely  from  the  cruor,  and,  therefore,  the 
albumen  they  noticed  may  belong  to  the  serum.     When 

*  Ann.  Philos.  iv.  139.  f  Hunter  on  Blood. 


97 

the  colouring  matter  of  the  blood  is  incinerated,  about  One 
third  per  cent.,  oxyde  of  iron  may  be  extracted  from  its 
ashes  ;  and  to  this  oxyde  has  been  attributed  'he  colour  of 
the  blood.  When,  however,  we  consider  its  very  small 
proportion,  and  the  fact  of  its  being  denied  to  exist  in 
blood  by  different  chemists,  there  will  appear  but  little 
reason  to  suppose  we  know  the  true  cause.  Berzelius 
found  the  ashes  to  amount  to  only  one  eightieth  of  the  co- 
louring matter,  and  of  this  there  is  not  more  than  one  half 
oxyde  of  iron  ;  he  is  also  of  opinion,  that  it  is  the  iron  itself, 
and  not  its  oxyde  which  exists  in  the  blood.*  Fourcroy 
analyzed  the  blood  of  a  human  fcetus,  and  found  mat  it 
differed  from  the  blood  of  the  adult  in  three  things  :  1.  Its 
colouring  matter  is  darker,  and  apparently  more  abundant; 
2.  It  contains  nofibrine,  but  probably  a  greater  proportion 
of  gelatine  than  the  blood  of  adults ;  3.  It  contains  no 
phosphoric  acid.t  The  absence  of  fibrine  may  be  owing 
to  the  rapid  formation  of  muscular  matter  at  this  time  of 
life ;  the  other  differences  must  also  depend  upon  fcetal 
peculiarities. 

Thus  we  have  a  view  of  the  materials  in  blood. 

Like  all  animal  substances,  albumen  is  capable  of  ex- 
isting in  various  states,  both  when  coagulated  and  ur.coag- 
ulated,  and  of  forming  a  number  of  distinct  species  ;  such 
as  the  curds  of  milk,  white  of  eggs,  and  that  in  the  blood. 
Coagulated  albumen  forms  an  essential  part  of  bone  and 
muscle  ;  brain  may  be  considered  as  a  species  of  it,  and  so 
may  the  lens  of  the  eye.  Cartilage,  nails,  horns,  and  hair, 
are  almost  entirely  composed  of  it.  It  forms  the  membra- 
nous parts  of  many  shells,  sponges,  &c.  and  is,  in  short, 

*  Ann.  Philos.  ii.  202.  t  Ann.  de  Chim.  vii.  162. 

13 


93 

one  of  the  most  general  and  important  of  the  animal  sub- 
stances.* Mr.  Hachett  has  shown  that  albumen  may  be 
converted  into  gelatine,  another  important  animal  produc- 
tion. Nitric  acid  has  this  power,  and  although  we  are  not 
to  suppose  that  the  same  operation  takes  place  in  the 
body,  we  learn  that  if  it  can  result  from  chemical  affinity, 
there  is  nothing  to  prevent  production  on  similar  princi- 
ples in  the  body.  Their  resemblance  is  more  strongly 
pointed  out  by  analysis. 


Carbon.    Oxygen.    Hydrog.  Nitrog. 


Gelatin, 
Albumen. 


47  8 
52  8 


27     2     7  9 
23  87     7  5 


16  9 
15  7 


X   =  100  parts- 


By  applying  the  atomic  theory  to  these  results,  it  ap- 
pears that  albumen  differs  from  gelatine,  by  having  two  ad- 
ditional atoms  of  carbon,  and  one  atom  less  of  hydrogen. 
Now,  we  know  that  respiration  has  the  power  of  subtract- 
ing carbon,  and  the  hydrogen  exists  in  every  animal  com- 
pound. 

The  fibrine  has  also  its  varieties,  and  constitutes  the  basis 
of  all  muscles.  For  this  purpose  it  seems  to  require  no 
further  change  from  the  state  in  which  it  exists  as  a  con- 
stituent of  blood,  than  to  become  more  firm  by  deposition. 
We  cannot  undertake  to  show  how  a  muscle  gets  its  shape, 
but  the  texture  of  fibrine  is  not  unlike  that  of  the  muscle 
when  well  washed  in  water.  We  may  even  conceive  in  a 
general  manner  how  its  structure  arises;  for,  in  every  in- 
stance, the  smallest  faciculus  of  fibrine  is  enclosed  in  a  co- 
vering of  cellular  matter,  which  is  principally  composed  of 
the  other  constituent  of  blood  ;  namely,  albumen.     When 

*  Thomson's  Chem. 


99 

they  are  both  thrown  out  by  the  arteries,  the  influence  of 
some  of  the  agents  (as  galvanismj  might  coagulate  the  lat- 
ter around  the  fibrine,  and  they  multiply  the  facicule.*  In 
short,  when  we  examine  the  muscular  structure,  these  two 
constituents  of  blood  will  be  found  to  occupy  almost  the 
entire  substance  including  blood  vessels  and  nerves.  The 
last  seems  to  be  nearly  constituted  by  albumen,  and  I  shall, 
subsequently,  show,  that  the  blood  vessels  have  their  ori- 
gin from  the  foregoing  ingredients.  It  would  occupy  too 
much  time  to  notice  all  the  animal  productions,  or  their 
shades  of  difference ;  I  shall,  therefore,  designedly  omit 
doing  so,  and  refer  to  Dr.  Thomson's  system  of  chemistry 
for  a  collected  account. 

As  to  the  principle  by  which  such  productions  are  ef- 
fected, although  it  is  not  in  our  power  to  offer  experimen- 
tal proof,  we  know  that  it  must  be  of  a  chemical  nature. 
No  other  agent  has  the  property  of  altering  chemical  com- 
position ;  and  some  of  these  very  animal  productions  have 
been  imitated  by  operating  chemically  on  others.  But  the 
vegetable  kingdom  offers  the  greatest  variety  of  examples  ; 
several  of  which  I  shall  now  mention.  1.  Oxalic  acid  may 
be  found  by  treating  sugar  with  nitric  acid.  2.  Camphor ; 
by  treating  oil  of  turpentine  with  muriatic  acid.  3.  Tan- 
nin; imitated  by  digesting  charcoal  in  nitric  acid.  4.  Su- 
gar; by  boiling  almost  any  animal  or  vegetable  substance  for 
several  hours  in  a  weak  solution  of  sulphuric  acid.  5.  Gum; 
may  be  formed  from  starch.  6.  Citric  acid;  from  the 
same  substance  by  chlorine.  7.  Saclactic  acid;  and 
8.  Malic  acid;  from  gum  by  nitric,  i).  Bitter  principle  of 
quassia    may    be    imitated    by   digesting    alcohol  some 

*  Sir  E.  Home  is  of  opinion  that  muscular  fibre  is  formed  by  the  serous 
globules.    (See  page  107.) 


100 

months  on  wheat  flour.  10.  Bird  lime,  by  fermenting 
the  middle  bark  of  holly,  and  then  boiling  the  residue  to 
dryness.  11-  Resin,  by  treating  bitumen  with  nitric  acid. 
12.  Extractive,  by  treating  guaiacum  with  the  same  acid,* 
&c.  &c.  These  are  considered  as  vital  productions,  and 
their  imitations  are  either  identical  in  external  and  chemi- 
cal characters,  or  so  nearly  so,  that  very  little  doubt  can 
be  left  of  their  chemical  formation  by  secretion.  It  may, 
however,  be  said,  that  this  conclusion  is  not  correct,  be- 
cause chemistry  has  not  produced  each  of  these  imita- 
tions from  the  flood  of  plants,  which  seems  to  be  done 
when  they  result  from  secretion,  and  it  may  be  de- 
nied that  one  secretion  is  at  any  time  formed  from 
another.  To  that  objection  it  may  be  answered,  that 
in  all  human  probability  it  will  never  be  in  the  power 
of  the  objector  to  prove,  that  nature  is  not  thus  imitated  ; 
and  therefore,  why  should  mere  doubt  on  that  subject  pre- 
vent our  adopting  a  position  which  is  strengthed  by  colla- 
teral proof?  My  object  in  this  essay  is  to  prove  by  phe- 
nomena, facts  and  analogy,  that  the  same  power  which  is 
so  astonishingly  active  in  searching,  as  it  were,  through 
matter  infinitely  more  compact  and  penetrable  than  orga- 
nised substances,  can  and  does  operate  in  the  different 
changes  of  life.  If  life  were  sufficient  to  perfect  our  struc- 
ture, why  should  so  much  of  it  be  hourly  cast  off?  What 
renders  such  rejected  parts  unfit  ?  No  agency  of  life,  most 
surely ;  it  is  the  action  of  substance  on  substance,  even  in 
the  midst  of  life.  It  is  true,  that  the  vital  phenomena  do 
not  depend  upon  the  mechanical  action  of  organs  alone, 
but  it  is  equally  true,  that  they  are  not  confined,  indepen- 
dent of  all  other  natural    agency,  to    a  vital    principle, 

*  Thomson's  Chem.  vol.  iv.  passim. 


101 

There  are  true  chemical  phenomena,  as  Fourcroy  re- 
marks, in  the  bodies  of  all  animals.  Products  and  changes 
result  from  the  intimate  attraction  which  governs  the  dif- 
ferent particles  composing  the  organic  tissue.  "  Liquids 
solidify  and  concrete,  while  solids  become  dissolved  by  the 
invariable  laws  of  solution  ;  salts  chrystalize  and  are  uni- 
ted one  to  the  other  ;  elastic  bodies  form  and  expand  in 
the  midst  of  cavities  and  dilatable  reservoirs.  In  the  most 
tortuous  ducts,  or  tubes  mucous  fluids  thicken  or  become 
more  fluid  ;  insipid  and  colourless  bodies  acquire  both  the 
opposite  qualities  :  oily  matter  is  produced  or  saponified  ; 
precipitations  are  formed  and  prevented  ;  salts  change 
their  bases  and  become  mutually  decomposed;  others  are 
constituted,  while  acids  are  formed  and  alkaline  or  metal- 
lic oxides  liberated."*  These  are  facts  which  no  one  of 
the  least  observation  can  doubt,  and  are  absolutely  demon- 
strative of  chemical  changes.  But  further,  we  find  com- 
pounds formed  in  the  living  body  precisely  of  the  same 
nature  as  invariably  results  from  chemical  union.  A  fair 
deduction  therefore  it  would  seem  must  be,  that  this  prin- 
ciple of  composition  guided  them  in  the  living  body  ;  thus 
we  find  iron,  mercury  and  other  metallic  substances  con- 
verted into  the  same  oxydes,  within  the  sphere  of  vitality 
as  they  are  when  exposed  to  chemical  action  without  it ; 
they  will  unite  to  ac'ds  just  as  well  in  either  situation.  So 
also  as  to  gases  >alts  and  acids.  The  ammonia  of  the  body 
is  the  same  as  that  of  the  laboratory  ;  and  if  we  analyze 
the  carbonic  acid,  carburetted  and  sulphuretted  hydrogen, 
nitrogen,  and  its  compounds,  the  phosphates,  muriates,  car- 
bonates, &c,  the  uncombined  acids  so  manifestly  and  fre- 
quently resulting  from  the  principles   of  life,  we  must  be 

*  Connaiss.  Chim. 


102 

convinced  that  they  were  formed  under  the  operation  of 
the  most  perfect  as  well  as  active  chemical  laws.  There 
are  other  substances  as  madder,  indigo,  garlic,  &tc,  which 
pass  into  the  circulation,  and  may  be  found  unaltered  in 
the  different  secretions.  A  theory  has  been  broached  to 
account  for  these  facts,  by  one  whose  ardour  in  favour  of 
sympathy  seems  to  have  carried  him  beyond  fair  reasoning 
or  probability  in  support  of  his  speculations.  Dr.  Chap- 
man, in  his  notes  to  Richerand's  physiology,  styles  the 
humoral  pathology  "  an  absurd  system ;"  and  in  his  zeal  for 
alteration  hazards  the  idea  "  that  the  process  of  assimila- 
tion, whether  performed  by  the  chylopoietic  viscera  or  by 
the  absorbent  apparatus,  completely  decomposes  all  sub- 
stances subjected  to  its  influence  ;  and  however  various 
in  their  principles,  reduces  them  to  one  homogeneous 
fluid,  bland  and  inoperative  in  its  nature,  or  in  other 
words,  renders  them  fit  for  the  purposes  of  nutrition. 
But  in  the  excretions  and  secretions,  beyond  the  sphere 
of  vital  powers,  chemical  action  takes  place  ;  by  which 
those  substances  are  in  part,  or  entirely  regenerated"  A 
few  remarks  will  show  how  very  little  is  gained  by  this 
substitute.  In  the  first  place,  chemistry  is  allowed  to  ex- 
ercise its  power  in  the  secretions,  which  is  really  more 
than  could  have  been  expected.  In  the  next  place,  we 
are  told  that  these  secretions  are  "  removed  beyond  the 
sphere  of  vital  functions;"  and  this  situation  may,  of 
course,  be  in  the  very  substance  of  a  gland.  It  is  in  these 
shrines  of  life,  then,  that  Dr.  Chapman  supposes  chemi- 
cal action  can  best  succeed.  Would  it  not  be  fair  (though 
the  contrary  was  meant  to  be  implied)  to  conclude,  there- 
fore, that  chemical  union  must  take  place  in  every  other 
part  of  the  living  body?  But  we  are  further  informed 
that  a  regeneration  of  the  same   substances,  as  were  re- 


103 

ceived  into  the  stomach,  takes  place  in  the  secretions^ 
which  we  are  in  the  habit  of  considering  as  onl\  parts  of 
the  assimilated  food.  And  yet,  though  at  first  thoroughly 
decomposed,  the  original  substances  can  be  regenerated 
after  their  constituents  have  circulated  through  the  body, 
and,  in  all  human  probability,  become  incorporated  in  the 
most  remote  extremities.  This  does  not  seem  much  short 
of  a  miracle.  If  I  did  not  fear  being  thought  disrespect- 
ful, I  should  say  it  could  only  be  accomplished  by  a  con- 
vention of  all  the  secreting  organs,  in  which  it  was  agreed 
that  common  stock  should  again  be  made.  But  even  then 
a  few  delinquent  organs  might  be  found  to  spoil  the  har- 
mony intended,  by  permitting  the  whole  of  their  share  of 
matter  or  workmanship  to  slip  out  of  the  body.  Any  one 
who  is  devested  of  prejudice  can  hardly  deny  that  the 
humoral  pathology  has  some  claims  to  attention ;  and  to 
abuse  the  whole  as  an  absurdity  because  somewhat  of 
this  may  be  traced  in  particular  expressions,  is  doing 
the  greatest  injustice  to  the  principle.  It  is  a  fact, 
that  where  any  change  of  composition  takes  place 
it  must  be  proximately  effected  by  the  inanimate  quali- 
ties of  matter.  I  do  not  deny  that  the  vital  structure 
renders  it  more  definite  of  a  final  end ;  but  it  is  by  the 
difference  of  its  chemical  agents  that  it  does  so.  How 
much  less,  then,  have  we  reson  to  detract  from  the  char- 
acter of  chemical  action  in  tubes  and  cavities  ?  All  glands 
are  composed  of  tortuous  tubes,  and  within  those  the 
changes  take  place  ;  the  length  and  conformation  of  such 
vessels  show  the  intention  to  be,  that  the  substances  shall 
act  by  their  chemical  power,  aided  by  those  which  they 
meet  on  their  way.  The  muscular  structure,  on  the 
other  hand,  seems  thrown  out  directly  from  the  delicate 
extremities  of  arteries,  because  as  the  fibrine,  albumen,  &c, 


104 

exist  already  formed  in  the  blood  they  require  little  else 
than  a  deposition  and  coagulation ;  and  certainly  are  not 
in  need  of  further  changes  of  composition  by  being  com- 
pelled to  react  in  tortuous  tubes  and  under  a  most  retarded 
circulation.  Another  circumstance  we  should  keep  in 
mind,  since  it  shows  the  existence  of  chemical  affinities  in 
these  situations.  Disease,  which  always  implies  debility  in 
the  vital  functions,  leads  to  the  greatest  variety  in  the  se- 
cretions, and  often  changes  the  character  of  any  one  so 
as  not  to  leave  a  doubt.  Now  if  such  secretions  depended 
upon  a  vital  power  alone,  its  deficiency  would  be  more 
likely  to  lessen  their  amount  than  change  their  ordinary 
qualities  ;  but  chemical  compounds  always  occur  in  the 
greatest  variety  when  the  substances  are  more  numerous. 
In  disease,  not  only  the  composition  of  the  blood  becomes 
altered,  but  during  its  disordered  circulation  materials  are 
crowded  together  which  otherwise  would  have  been  lo- 
cated in  various  parts  of  the  system.  Under  such  circum- 
stances the  chemical  character  of  the  secretions  becomes 
more  remote  from  those  which  depend  upon  the  regula- 
lated  function.  During  that  disease,  known  by  the  name 
of  diabetes,  in  which  the  urine  is  excessive  in  quantity, 
the  serum  of  blood  often  assumes  the  appearance  of  whey; 
and  Dr.  Wollaston  has  shown  that  it  contains  no  percep- 
tible quantity  of  sugar,  even  when  the  urine  is  loaded  with 
it.*  These  remarks  must  suffice,  since  little  definite  in- 
formation can  be  offered  ;  but  I  apprehend  that  whatever 
may  be  the  peculiarity  of  the  vital  arrangement,  its  mate- 
rial productions  must  invariably  result  from  true  chemical 
affinity,  promoted  by  some  or  all  of  the  agents  mentioned 
in  the  former  part  of  this  essay. 

*  Thomson's  Chera,  book  5. 


105 


FIGURE. 


Upon  this  subject  the  late  experiments  of  Sir  Everard 
Home  will  be  found  more  curious  and  important  than  any 
of  which  I  am  at  present  aware  ;  they  must  also  constitute 
the  entire  subject,  since  I  am  desirous  of  confining  this 
essay  to  as  limited  a  form  as  possible.  It  is  well  known 
among  the  numerous  original  ideas  of  Mr.  Hunter,  that  he 
maintains  that  the  blood  formed  its  own  vessels  independ- 
ent of  any  communication  with  those  already  existing ; 
or,  in  his  own  words,  that  "  the  blood  moves  in  the  living 
solids  which  it  both  forms  and  supports,"  and  that  "  when 
new  vessels  are  formed,  they  are  not  always  elongations 
from  the  original  ones,  but  vessels  newly  formed,  which 
afterwards  open  a  communication  with  the  original."  Now, 
although  we  may  suppose  the  blood  to  have  irritability, 
(which  is  what  the  author  implies,  and  which  in  my  opi- 
nion is  perfectly  reasonable,)  without  conceding  to  the 
ironical  language  of  Mr.  John  Bell,  that,  therefore,  "  it 
should  have  the  privilege  of  knowing  when  to  exert  itself,'* 
or  "  that  it  should  have  some  kind  of  intelligence  or  con- 
sciousness, by  means  of  which  it  could  understand  when 
it  were  within  and  when  without  the  body  ;  and  whether 
in  certain  circumstances,  it  were  fit  that  such  vessels  should 
be  formed."  Intelligence  can  only  exist  in  complete  living 
systems  ;  and  there  are  thousands  apparently  without  it 
which  have  both  irritability  and  definite  functions.  This 
quality  is  never  a  character  of  detached  parts,  even  of  the 
brain,  which  is  its  seat.  The  irritability  of  a  finger  just  cut 
off  is  as  great  as  before  the  operation,  and  its  organization 
is  infinitely  better  adapted  for  the  exercise  of  sensibility, 
(since  it  possesses  nerves)  than  the  blood  ;  yet  we  cannot 

14 


106 

be  so  forgetful  of  this  property  as  to  suppose  that  the  dis- 
jointed finger  possesses  the  least  extent  of  it.  The  fol- 
lowing experiments  will  show  that  the  blood  does  produce 
its  own  vessels,  and  that  too  by  the  agency  of  its  chemical 
and  physical  properties. 

In  Sir  Everard  Home's  paper  upon  coagulation  (croonian 
lecture*)  we  find  the  following  account  of  blood  taken 
from  his  own  arm.  "  In  about  five  minutes  something 
was  seen  to  be  disengaged  in  different  parts  of  the  coagu- 
lum,  (beginning  to  show  itself  where  the  greatest  number 
of  globules  were  collected  ;)  and  from  thence  passing  in 
every  direction  with  considerable  rapidity  through  the  se- 
rum, but  not  at  all  interfering  with  the  globules  themselves, 
which  had  all  discharged  their  colouring  matter.  Where- 
ever  this  extricated  matter  was  carried,  a  net-work  imme- 
diately formed,  anastimosing  with  itself  on  every  side,  and 
through  every  part  of  the  coagulum.  When  the  parts  be- 
came dry,  the  appearance  of  a  net  work  remained  unal- 
tered. In  some  instances,  bubbles  were  seen  to  burst 
through  the  upper  surface  of  the  coagulum  ;  this,  how- 
ever, did  not  prevent  the  ramifications  that  have  been 
described,  from  taking  place.  These  changes  were 
observed  with  strict  attention  through  a  microscope.  Sir 
Everard  Home  has  presented  engravings  of  their  appear- 
ance, and  it  is  absolutely  impossible  to  overlook  the  strong 
resemblance  which  they  bear  to  designs  of  organized  sub- 
stances. This  gentleman  further  remarks,  that  "  if  the 
blood  is  cold  when  it  is  exposed  in  the  microscope,  and 
there  is  a  large  quantity  of  serum  on  the  glass,  the  net 
work  is  only  formed  in  those  parts  where  clusters  of  glo- 
bules are  collected,"  and  further,  that  "  when  clear  serum, 

*  Phil.  Trans,  for  1818. 


107 

without  any  globules  is  put  upon  the  glass,  nothing  is  ex- 
tricated. In  this  paper  it  is  also  shown  that  after  blood 
had  remained  extravasated,  and  become  vascular,  a  short 
time  was  sufficient  to  make  them  become  regular  tubes, 
having  distinct  and I  separable  coats.  From  these  facts  :e 
learn  that  a  gas  forms  the  blood  vessels  with  their  ramifica- 
tions, and  that  it  originates  from  the  serous  globules.  This 
shows  that  these  globules  undergo  chemical  changes;  not  ac- 
cidentally or  in  a  limited  number,  since  the  passage  form- 
ed by  some  of  the  gas  through  the  upper  surface  of  the 
coaguluni,  did  not  put  a  stop  to  the  tubular  formation. 
This  gas  was  determined  to  be  carbonic  acid;  which 
whether  it  was  derived  from  the  serous  globules  or  from 
different  parts  of  the  body  during  circulation,  is  always, 
in  organic  matter,  a  proof  of  chemical  changes.  Their 
utility  in  the  production  of  blood  is  made  manifest  by  an 
experiment  of  Sir  E.  Home,  instituted  for  the  purpose ; 
he  "  placed  a  vessel  nearly  filled  with  blood  drawn  from 
the  arm,  under  the  receiver  of  an  air  pump,  and  by  ex- 
haustion, extracted  the  gas  contained  in  the  blood.  This 
blood  deprived  of  its  gas,  when  coagulated,  exhibiting 
no  appearance  of  net  work.  In  that  part  which  had  co- 
agulated before  the  exhaustion  was  completed,  the  net 
work  was  beautifully  distinct."  This  gentleman  injected 
these  vessels,  and  concludes,  that  "  as  the  injection  could 
only  fill  the  spaces  from  which  the  carbonic  acid  gas  was 
extracted,  it  cannot  be  doubted  that  the  channels  were 
formed  by  the  gas."  Sir  Everard  Home  also  mentions 
the  previous  experiments  of  Mr.  Bauer,  which  confirm  the 
foregoing  rationale  by  showing  a  similar  process  for  vege- 
table formation.  "  In  his  close  attention  to  the  changes 
that  took  place,  he  was  very  much  struck  with  the  rapid 
increase  of  the  tubular  hair  of  the  root  of  a  young  plant 


108 

of  wheat,  in  its  earliest  stage  of  vegetation ;  and  fixing  his 
whole  attention  upon  that  part  of  the  plant,  he  observed 
small  pustules  of  a  slimy  substance  arising  under  the  epi- 
dermis, on  the  surface  of  the   young   root.     In   a   few 
seconds,  a  small  bubble   of  gas  burst  from  the  root  into 
the  slimy  matter,  which  it  extended,  in  a  moment,  to  the 
length  the  hair  was  to  acquire  ;  and  the  slimy  matter,  sur- 
rounding the  gas,  immediately  coagulated,  and  formed   a 
canal.     He  repeated  his  observations  on  another  plant, 
whose  pubescence  consisted  of  a  jointed  hair,  and  obser- 
ved the  same  effect  to  take  place ;  a  bubble  issued  from 
the  young  stalk,  and  extended  the  slimy  mucus  to  a  short 
distance,  forming  the  first  joint,  which  immediately  coagu- 
lated and  became  transparent :  at   its  extremity,  a  new 
pustule,  of  the  slimy  mucus,  accumulated,  into  which,  in 
a  short  time,  the  gas/rom  the  first  joint  rushed,  and  then 
in  a  moment  a   second  joint  was  formed.     In  the  same 
manner  he  observed  the  formation  of  ten  or  twelve  joints 
to  take  place."  It  now  only  remains  to  show  that  the  ana- 
logy is  as  manifest  in  pus  which  is  known  to  be  secreted 
for  the  object  of  granulation.     For  which  purpose  I  ^hall 
continue  Sir  Everard  Home's  experiments  as  he  describes 
them.*     '•  As  the  globules  of  pus  are  similar  to  those  of 
the  blood,  I  made  experiments   upon   the  fluid  in  which 
they  are  suspended,  and  found  inspissation  to  produce  the 
same  effect  on  if  as  coagulation  does  on  the  other ;  that  a 
similar  net-work  is  formed,  and  apparently  by  the  same 
means  (since,  if  pus  is  deprived  of  its  carbonic  acid  gas,  of 
which  it  contains  a  large  quantity,  by  exhaustion  in  the 
air  pump,  no  such  net-work  takes  place.)     This  is  a  fact 
of  considerable  importance  in  practical   surgery ;  for  as 

*  Phil.  Trans,  for  1819. 


109 

we  know  that  inspissated  pus  can  become  vascular,  simi- 
lar to  coagulated   blood,  we  have  arrived  at  the  principle 
on  which  granulations  depend,  and  from  whence  they  de- 
rive the  power  of  contraction  which  is  found  to  be  inhe- 
rent in  them.     We  also  can  account  for  the  great  advan- 
tage of  compression   on  the  surface  of  soies;  since,  by 
that  means,   all  the   superfluous  pus  is  removed,  leaving 
only  enough  for  inspissation,  in  which  state  the  carbonic 
acid  gas  is  extricated,  forming  channels  so  as  to  admit  of 
its  becoming  afterwards  vascular,   and  then  taking  on  the 
form  of  healthy  granulations.     Sir   Everard  Home  con- 
cludes that  the  pus  is  turned  into  new  flesh,  and  offers  the 
following  facts.     A  healthy  sore,  when  examined  with  a 
microscope,  had  the  eminences  on  its  surface  (these  were 
apparently  composed  of  small  clusters  of  tortuous  blood- 
vessels ;)  the  hoilows  were  rilled  with  pus.     After  five  or 
ten  minutes'  exposure,  a  very  thin  transparent  pellicle   co- 
vered the  whole  surface,  while  bubbles  of  gas  were  seen  to 
make  their  appearance  in  different  places.     In  a  few  mi- 
nutes,  more  blood  entered  and  diffused  itself  through  the 
net-work  of  vessels,  (formed  by  the  gas,)  which  at  this  time 
were  so  weak,  that  putting  the   foot  with  the  sore,  to  the 
ground,  ruptured  them.     These  canals,  however,  though 
so  weak  on  the  first  day,  were  found  on  the  second  to  have 
become  permanent   tubes,  covered  over  by  cuticle.     The 
degree  of  coagulation  determines  the  extent  of  vascularity  ; 
this  fact  was  proved  by  the  addition  of  muriate  of  ammo- 
nia as  well  as  cold  water,  which  have  the  property  of  pro- 
ducing coagulation  much  more  speedily  than  atmospheric 
air.     Sir  Everard  Hom^  supposes  that  the  blood  (having  a 
strong  affinity)  absorbs  the  carbonic  acid  gas   as   it  enters 
these  newly  tormed  vessels.     This  gentleman  shows  the 


110 

following  reasons  for  supposing  that  the  muscular  fibre  is 
made  from  the  globules  of  the  blood.* 

1.  The  fibre  can  be  separated  until  it  appears,  by  mi- 
croscopic measurement,  not  larger  in  diameter  than  those 
globules  of  blood.  2.  Muscular  fibre,  when  thus  dissect- 
ed, appears,  through  the  microscope,  as  compocud  of 
globules  so  as  to  form  a  line.  3.  The  globules  of  bl>  od, 
when  deprived  of  their  colouring  matter,  (which  envelops 
them,  and  is  three  times  as  great,)  while  floating  in  the  se- 
rum, are  seen  to  have  an  attraction  toward  ope  another, 
and  to  unite;  but  "  that  while  the  globules  are  enveloped 
in  their  colouring  matter,  they  are  not  seen  to  run  together 
and  coalesce  with  one  another  in  the  field  of  the  micro- 
scope. It  is,  therefore,  probable,  that  the  attraction  by 
which  this  effect  is  produced  only  takes  place  between 
globules  deprived  of  their  colour." 

Thus  have  we  seen  that  the  agents,  the  matter,  and  the 
productions  of  life,  are  chiefly  referible  to  the  phenomena 
of  chemistry.  This  ascendancy  is  not  confined  to  the  be- 
ginning or  end  ;  we  must  notice  its  progress  through  every 
stage,  even  from  the  first  dawn  of  animated  existence. 
Regulated  by  the  most  inconceivable  wisdom,  life  is  sus- 
tained by  the  universal  laws  of  nature;  and  if  our  pride 
fondly  gazes  at  the  mystery  of  generation  let  us  also  learn 
to  be  instructed  by  the  extinction  of  life;  and  instead  of 
overrating  our  own  conformation,  let  us  reverence  the 
wrisdom  which  can  cause  life  to  arise,  and  be  guided  by  the 
universal  laws  of  matter ! 

I  shall  now  enter  upon  an  inquiry  into  life  itself;  and 
in  doing  so  the  truth  shall  alone  be  sought  after,  without 
reference  to  opinion  or  prejudice. 

*  Phil.  Trans,  for  1818. 


Ill 


ANIMATION. 


In  collecting  together  the  phenomena  of  assimilation^ 
numerous  obstacles  must  ever  oppose  themselves.  The 
firs',  combinations  of  matter  are  so  extremely  minute  that, 
in  all  human  probability,  the  commencement  of  organiza- 
tion wiil  never  be  perceptible.  All  that  the  eye  can  do 
is  to  observe  its  growth  ;  and,  at  the  earliest  period  of  this 
advantage,  life  is  found  already  to  exist.  It  is  for  this  rea- 
son chiefly,  that  the  origin  of  vitality  lies  so  deeply  ob- 
scured. Our  conclusions,  at  present,  must  be  governed 
by  analogy  and  general  views  ;  and  although  the  evidence 
which  thus  results  is  not  of  the  highest  degree,  it  is  cer- 
tainly entitled  to  be  next,  By  such  means,  though  with 
more  certainty,  the  existence  of  a  Supreme  Director  is 
demonstrated  when  the  works  of  nature  are  surveyed. 

The  inquiry  whether  animation  can  result  from  any 
possible  modification  in  the  composition  of  inanimate  mat- 
ter, has  frequently  entered  into  metaphysical  discussions. 

I  must  confess  it  has  often  astonished  me  how  very 
easily  satisfied  some  inquirers  have  been.  A  view  limited 
to  three  or  four  properties  of  matter,  such  as  dimension, 
figure,  or  weight,  have  been  twisted  into  every  form,  and 
when  these  failed  to  give  life,  the  subject  has  been  con- 
sidered as  examined  But  who  has  ever  investigated  the 
chemical  laws  to  their  full  extent,  or  brought  to  view  the 
incalculable  variety  of  its  products  ?  These  surely  can 
never  be  overlooked  when  we  are  surveying  the  property 
of  matter  ;  and  ages  will  roll  by  before  any  mortal  can 
experimentally  deny  their  power.  But  it  appears  to  me 
that  the  solution  can  never  result  from  a  consideration  of 
the  properties  of  matter  alone ;  other  circumstances  full 


112 

as  imperious  must  be  thoroughly  understood,  and  these 
are  so  numerous  as  to  render  general  reasoning  unfounded. 
We  are  in  the  habit  of  saying  one  body  has  the  power  of 
uniting  to  another,  but  we  speak  incorrectly,  or  rather  pre- 
suppose other  agents.  A  familiar  example  will  illustrate 
my  meaning*  Sulphuret  of  iron  is  weli  known  to  be  a 
material  product,  or,  in  other  words,  proximately  formed 
by  the  laws  of  matter ;  yet  with  all  this  certainty  we  can- 
not suppose  that  it  invariably  results  from  these  laws 
alone.  Although  the  constituents  possess  a  perfect  affini- 
ty for  each  other,  they  have  no  inherent  power  sufficiently 
strong  to  bring  them  together  when  outside  of  the  least 
perceptible  distance.  The  same  circumstance  takes  place 
in  all  chemical  compounds.  Let  the  power  for  union  be 
ever  so  strong,  their  presence  is  also  requisite,  and  this 
never  proceeds  from  their  material  properties ;  they  also 
depend  on  agents,  such  as  temperature,  solution,  tritura- 
tion, and  a  thousand  others  emanating  from  the  laws  of  the 
universe.  Hence  then  though  animation  should  proceed 
from  the  proximate  influence  of  material  properties,  we 
cannot  limit  it  to  these  alone.  If  conclusions  are  to  be 
drawn,  they  should  be  founded  upon  the  phenomena  of 
vitality,  which  are  daily  passing  before  our  eyes,  and  speak 
true  knowledge  to  the  understanding.  We  ought  ever  to 
be  guided  by  what  we  know,  and  that  range  is  too  limited 
to  attempt  to  draw  general  conclusions  from  the  properties 
of  matter.  It  is  impossible,  at  present,  to  demonstrate  unde- 
niably the  correctness  of  either  opinion;  the  object  of  this 
essay  is  to  bring  forward  facts  which  have  a  tendency  to 
show  the  connexion  of  chemistry  with  animated  matter. 
The  remarks  of  Buffon  "  that  the  reproduction  of  an 
animal  or  vegetable  cannot  be  explained  in  a  satisfactory 
manner,  if  a  clear  idea  of  the  operation  of  nutrition  is  not 


113 

obtained,'*  seem  to  me,  to  be  forcibly  true.     Nothing  can 
be  more  analogous  to  the  production  of  life  than  its  subse- 
quent  support;  I  shall   accordingly  commence  with    this 
view.     BufFon,*  founded  his  theory   of  nutrition  upon  the 
idea,  "  that  there  exists  an   infinity  of  living  organic  par- 
ticles in  nature  ;  that  their  production  is  of  little  expense 
to  nature,  since  their  existence  is  constant  and  invariable  ; 
and  that  the  causes   of  death  on'y  separate  without  de- 
stroying them.     Therefore  the  matter  which  an  animal  or 
vegetable   assimilates,  is   an  organic   matter  of  the  same 
nature  as  the  animal  or  vegetable  itself,"     This  observa- 
tion is  undoubtedly  true  with  one  exception.     It  is  impos- 
sible  to  admit  the  "  constant  and  invariable"  existence  of 
any  living  particle;  the  supposition  is  directly  contradict- 
ed by  the   most  superficial  view  of  matter.     But  on  the 
other  hand  we  must  admit  that  the  particles  of  assimilated 
nutriment  are  endowed  with  as  much  vitality  as  any  which 
constitute  the  body  itself.     Hence  this    naturalist  drew  a 
correct  conclusion  when  he   remarked   that   "  the  matter 
which  an   animal  or  vegetable  assimilates,  is  an  organic 
matter  of  the  same   nature,  as  the  animal  or  vegetable  it- 
self."    This   however  is  very  far  from  the  view  which  he 
wished  to  inculcate.     But  what  can  be  more  inconsistent 
with  observation  than  to  suppose  that  the  generation  of  an 
animal  or  vegetable  depends  upon  the  union  of  living  par- 
ticles, which  existed  with  this  characteristic  since  creation 
began,  and  that  death  only  separates  (hem  without  destroy- 
ing their  vitality  ?  Such  a  theory,  though  endowing  matter 
so  profusely,  c  uld  not  reserve  for  itself  one  living  parti- 
cle to  sustain  its  own  existence,  and  has  not  been  able  to 
survive   the  author  whose   brain  was  the   most   congenial 

*?afarai  History. 
1.5 


114 

hot  bed  that  it  ever  had.  We  may  presume  therefore 
that  an  absolute  extincton  of  life  does  take  place;  let  us 
now  apply  this  fact. 

The  nutriment  which  supports  the  body  by  adding  living 
matter,  was  previous  to  its  changes  during  assimilation 
perfectly  inanimate.  How  can  we  consistently  account 
for  the  acquisition  of  this  vital  property,  without  attribut- 
ing it  to  the  changes  of  composition  occurring  during  that 
process  ?  These  we  have  already  shown  to  be  of  a  chemical 
nature  ;  and  we  are  not  justified  in  doubting,  until  at  least 
as  strong  evidence  of  contrary  nature  shall  point  an  ex- 
planation of  the  phenomena.  But  let  us  examine  the  sub- 
ject closer.  There  is  not  the  slightest  proof  that  nutri- 
ment can  be  thus  endowed  by  mere  contact  with  living 
matter,  independent  of  such  changes  of  composition  ;  and, 
if  we  rely  upon  general  reasoning,  we  must  be  convinced 
that  it  does  not.  In  the  first  place,  the  existence  of  the 
phenomena  decidedly  points  out  the  necessity  of  such 
changes;  and  in  the  next,  it  is  perfectly  in  contradic- 
tion to  our  knowledge,  to  maintain  that  life  can  be  trans- 
ferred from  substance  to  substance,  by  simple  juxtapo- 
sition. Irritability,  which  is  all  the  life  we  can  suppose, 
when  characterising  a  substance,  may  impart  motion  to  a  fo- 
reign body  in  conjunction,  while  that  situation  remains  ; 
but  to  endow  this  last  with  its  own  properties  is  far  different. 
It  is  absurd  to  suppose  that  this  property  which  depends 
upon,  and  is  limited  to,  the  matter  possessing  it,  can  act 
beyond  that  matter,  But  let  us  entertain  a  proper  idea  of 
irritability,  or  even  its  more  complicated  forms  constitu- 
ting the  living  system.  Has  it  any  existence  without  the 
application  of  a  stimulus  ?  Not  the  slightest.  When  we 
take  a  muscle  and  excite  its  contractions,  we  are  correctly 
satisfied  that  it  is  then  alive.     Without  an  exciter  we  never 


115 

could  suppose  it,  and  when  that  exciter  is  removed  we 
have  no  right  to  do  so,  for  it  is  unequivocally  dead.  Hence, 
then,  we  learn,  that  life  is  an  effect  depending  upon  at  least 
two  inanimate  substances  having  a  peculiar  chemical  and 
physical  composition.  Hence,  also,  we  learn,  that  irrita- 
bility has  no  influence  beyond  these  limits,  and  that  when 
it  can  be  manifested  in  adjoining  matter,  it  must  originate 
upon  the  same  principles,  independent  of  any  connexion. 
We  are,  therefore,  I  think,  entitled  to  consider  that  irrita- 
bility does  arise  in  the  assimilated  nutriment,  by  mere 
contact  with  the  living  solids.  But  there  is  a  degree  of 
evidence  that  this  property  is  acquired  before  any  such 
union  takes  place.  The  substance  of  the  blood  is  un- 
doubtedly derived  from  the  nutriment ;  therefore,  all  Mr. 
Hunter-s  arguments  for  its  vitality,  (and  which  an  eminent 
writer  considers  as  "  the  best  established  doctrine  of  mo- 
dern physiology,"  must  confirm  the  origin  of  this  property. 
The  iibrine  has  also  been  found  irritable  by  the  experiments 
of  Circaud  and  Delametherie  j*  which  seems  to  prove 
that  this  property  is  acquired  during  circulation.  After 
this  shall  it  be  denied  that  assimilation  is  of  a  chemical 
nature  ?  This  would  indeed  be  contending  for  argument 
sake.  There  is  not  only  direct  evidence  that  the  blood 
undergoes  true  chemical  changes ;  (see  respiration  ;)  but 
the  total  difference  in  composition,  between  chyle  and  the 
food,  leaves  scarcely  a  doubt.  (See  digestion.)  If  the 
property  of  irritability  does  not  proceed  from  chemical 
changes  in  our  food,  why  should  the  rejection  of  any  be 
necessary  ?  Why  should  this  excess  of  matter  so  mani- 
festly useless,  be  at  any  time  the  result  of  a  vital  process  ? 
The  most  rational  answer  seems  to  be,  that  vitality  is  de- 

*  See  page  13.  ante. 


116 

pendent  upon  a  peculiarity  of  chemical  composition,  and 
that  such  substances  as  are  formed  by  too  powerful  an  affi- 
nity to  admit  of  decomposition  in  the  body,  can  never,  by 
any  vital  process,  residing  in  that  body,  be  rendered  sus- 
ceptible of  animation.  The  foetal  blood  is  allowed  not  to 
be  coeval  with  the  first  organization  which  is  the  rudiment 
of  the  original  vital  foundation  ;  hence  this  blood,  as  well 
as  its  irritability,  must  be  generated. by  chemical  changes 
effected  in  the  matter  constituting  nourishment  at  this 
early  period  of  imperfect  existence.  Lastly  ;  Sir  Eve- 
rard  Home's  paper  shows,  that  granulation  and  the  forma- 
tion of  blood  vessels,  which  cannot  be  excluded  from 
vitality,  depend  upon  a  combination  of  the  physical  and 
chemical  properties  of  the  blood,  or  pus  in  animals,  and 
the  sap  in  plants.*  Irritability,  like  a  chemical  property, 
depends  upon  composition  more  than  dimension  or  figure  ; 
if  the  substance  capable  of  exhibiting  it  be  divided  into 
pieces,  the  property  is  not  extinguished  ;  but  when  treated 
with  a  chemical  agent  it  is  destroyed  in  proportion  to  the 
extent  and  perfection  of  its  power.  Thus  we  have  exhi- 
bited an  instance  where  vital  matter  originates  independ- 
ent of  the  generative  process  ;  and  have  shown  reason  for 
supposing  that  it  depends  upon  chemical  composition.  Let 
us  point  out  a  few  more  important  considerations. 

John  Hunter  supposes  that  the  blood  forms  its  own  ves- 
sels ;f  all  practical  observation  must  lead  us  to  the  same 
conclusion.  When  a  piece  is  cut  out  from  a  nerve,  we 
know  that  it  becomes  filled  up  so  as  to  render  that  nerve 
complete  or  nearly  so,  "by  means  of  the  blood  forming  a 
union  of  coagulum :;  and  that  the  coagulum  becomes  more 
and  more  of  the  texture  5"  but  what  assimilating  or  se- 
creting vessels  are  [here  in  this  coagulum  to  effect  such  a 

*  See  nase  103.  ante,  t  On  the  Blood, 


117 

change,  unless  those  formed  of  itself  ?  Those  that  belong 
to  the  sound  portions  may  even  send  proper  matter;  but 
if  these  are  supposed  to  have  no  power  of  extension,  as 
Mr.  Hunter  remarks,  we  must  suppose  that  all  vascular 
apparatus  which  afterwards  gives  this  coagulum  the  pro- 
perty of  a  nerve,  is  formed  by  the  coagulum.  But  this  I 
shall  not  consider  important  to  establish,  since  the  polypus 
and  other  animals,  the  umbilical  chord  as  well  as  all  the 
vegetable  kingdom  show  that  animation  may  exist  without 
nerves*  Sir  Everard  Home's  experiments  on  blood  and 
pus  prove  that  blood  vessels  are  formed  by  the  blood,  inde- 
pendent of  nerves  or  any  necessary  connexion  with  the 
body  His  experiments  also  led  him  to  suppose  that  flesh 
is  formed  by  pus.  If  these  facts  be  extended  what  do  they 
lead  to  ?  Why,  that  all  the  other  parts  contained  therein 
have  a  similar  origin,  and  that  granulation  is  in  the  end  but 
a  process  of  union  by  the  first  intention,  since  new  vessels 
are  united  to  the  old  ones  by  contact.  We  have  seen  that 
pus  forms  the  blood  vessels  and  flesh  for  such  a  breach  ; 
what  more  vital  or  important  parts  can  any  structure  have 
than  these  ?  Surely  we  can  have  but  little  doubt  concern- 
ing the  origin  of  the  minor  apparatus  such  as  absorbents. 
One  other  consideration  strongly  confirms  the  foregoing. 
If  any  system  of  vessels  is  always  necessary  to  form 
another,  how  is  the  first  set  supported  ?  if  by  another,  how 
is  this  last  supported  ?  we  must  introduce  another  and 
another  set,  until  they  are  brought  to  atomic  magnitude, 
and  even  then  nothing  will  be  gained  since  the  very  last 
must  have  its  system  of  supporting  vessels.  We  shall 
inevitably  come  to  the  conclusion  that  one  whole  set  origi- 
ninates  from  the  blood  without  any  vascular  apparatus. 
This  may  seem  too  extensive  for  admission  ;  but  the  reason 
is  that  we  confine  our  view  to  the  most  complex  stage. 


118 

All  that  we  now  gaze  at  with  wonder,  was  once  simple 
and  limited  ;  where  mutual  assistance  was  either  feeble 
or  extinct.  Can  we  then  hesitate  in  believing  that  when 
such  a  limited  vascular  system  originates  independently 
of  any  other,  it  can  become  complex  and  extensive  by  a 
continuation  of  arrangement  ?  Hence  then  we  learn  that 
the  blood  or  something  similar  is  qualified  to  form  all  the 
parts  of  a  complex  system  ;  how  much  more  qualified, 
then,  must  it  be  to  form  the  simplest  circulating  apparatus, 
without  nerves,  and  conducing  to  the  support  of  the  most 
limited  animation  ?  Let  us  now  examine  of  what  nature 
blood  must  be   for   this    purpose. 

We  have  seen  that  changes  of  composition  in  inanimate 
matter  (during  digestion,  respiration,  he.)  give  rise  to  the 
formation  of  blood ;  therefore  wherever  these  exist,  under 
such  circumstances  (which  are  undoubtedly  dependent  up- 
on chemical  affinity)  life  may  result.  We  are  too  much  in 
the  habit  of  confining  our  attention  to  the  origin  of  blood  in 
adults  ;  let  us,  therefore,  turn  to  the  human  embryo  or  the 
chick  in  ovo.  The  embryo  has  been  supposed  to  have  an  in- 
dependent circulation;*  and  this  opinion  is  supported  by  di- 
rect analogy  from  the  egg  or  seed.  How  then  does  it  even 
accumulate  its  blood,  since  it  performs  neither  digestion  nor 
respiration  ?  Certainly  not  by  the  process  of  an  adult.  But  if 
the  human  embryo  be  supposed  to  receive  its  nourishment, 
assimilated,  from  the  mother,  we  will  abandon  the  instance 
and  bring  forward  the  chick  in  ovo,  where  no  connexion 
whatever  exists.  In  this  no  material  assimilation,  no  di- 
gestion or  respiration  seem  to  take  place  when  the  blood 
appears  at  the  punctum  saliens  ;  its  origin,  or  at  least  ac- 
cumulation, must  be  from  beginning  to  end,  from  the  egg 

Dr.  Chapman  on  foetal  nourishment, 


119 

substance,  and  that  too  without  any  vital  apparatus,  (in 
appearance)  sufficiently  vigorous  to  have  an  agency.  To 
this  instance  I  will  add  the  seal  in  which  we  must  suppose 
the  power  of  life  infinitely  more  simple.  From  such  con- 
siderations we  should  be  inclined  to  believe,  that  blood 
may  originate  without  the  aid  (in  the  commencement)  of 
a  vital  structure.  It  is  not  necessary  that  this  should  be 
blood  of  our  bodies,  or  even  the  same  as  first  becomes 
visible  in  the  chick.  The  fluid  which  originates  in  the 
seed  or  plant  is  totally  dissimilar  and  yet  it  produces  ves- 
sels and  all  the  vital  structure ;  neither  is  pus  or  serum 
exactly  the  same  though  possessed  of  such  a  power. 
Hence  we  learn  that  a  vital  structure  may  be  formed  by 
other  than  the  complete  blood,  and  life  exist  or  be  sup- 
ported. To  recapitulate  :  All  the  foregoing  observations 
intimate  that  a  fluid  (analogous  to  blood)  of  variable  nature, 
maybe  formed,  (to  appearance,  without  a  vital  agency, 
and  principally  from  combinations  of  inanimate  matter,) 
which  shall  have  the  power  of  forming  a  vital  apparatus, 
provided,  always,  that  circumstances  which  are  not  pecu- 
liar to  life  shall  be  favourable.  It  will  now  be  my  object 
to  bring  forward  instances  which  have  been  considered 
favourable  to  such  opinion  ;  and  it  is  to  be  remarked  that, 
throughout,  nothing  but  the  very  simplest  organization 
will  be  found  to  exist.  When  parts  of  plants  or  animals 
(which  undergo  ready  decomposition)  are  infused  in  water 
and  well  corked  up  in  a  phial,  animalculse  invariably  ap- 
pear after  a  few  days.*  This  experiment  is  easy  of  suc- 
cess, and  the  following  facts  have  been  found  to  follow  : 
That  it  makes  little  or  no  difference  whether  the  organic 
matter  be  infused  in  its  natural  state  ;  or  whether,  boiled, 

*  Needham  on  Tnfusions. 


J  20 

roasted,  or  otherwise  exposed  to  an  elevation  of  tempera- 
ture sufficient  to  destroy  all  the  forms  of  life,  with  which 
we  are  acquainted  :  The  animalculae  still  appear  during 
corruption. 

That  this  generation  takes  place,  particularly  in  jelly, 
(even  after  having  been  roasted  or  boiled,)  though  trans- 
fered  as  rapidly  and  guardedly  as  possible. 

That  it  only  takes  place  in  such  matter  as  can  undergo 
what  is  considered  spontaneous  decomposition. 

That  the  animalculae  are  always  multiplied  in  proportion 
to  the  extent  of  that  decomposition. 

That  they  are  generated  throughout  the  matter ;  even  in 
parts  which  have  not  been  exposed  to  the  air  ;  as  when  a 
mass  of  jelly  is  thrown  into  boiling  water,  to  make  the 
infusion. 

That  chemical  agents  are  always  necessary,  &c.  &c. 

In  opposition  to  the  apparent  deduction  of  these  facts, 
it  has  been  supposed  that  eggs,  conveyed  through  the  me- 
dium of  the  air  or  water,  are  always  deposited  on  the  or- 
ganized matter  previous  to  corruption  ;  and  that  chemical 
combinations,  though  absolutely  essential,  do  not  give 
rise  to  animation,  (which,  however,  seems  to  consist  of  lit- 
tle more  than  irritable  motion.)  This  supposition,  it  is  to 
be  remarked,  has  no  solid  foundation ;  no  eye  has  ever 
seen  such  eggs  either  in  the  air,  water,  or  the  corrupted 
matter,  which  is  considered  as  a  mere  nidus.  Neither 
can  it  be  presumed  that  such  eggs  are  of  greater  magni- 
tude than  the  animalculae;  many  of  which  are  only  visible 
during  motion.  Even  Leuwenhock's  statement  is  more 
rational,  when  he  contended  that  he  could  distinguish  the 
sexes  of  the  animalculae,  for  he  actually  saw  something* 
But  allowing  (for  the  sake  of  investigating  truth)  that 
there  are  eggs  thus  deposited,  can  we  indulge   the  belief 


121 

that  they  will  be  able  to  survive  roasting  or  boiling  ?  They 
certainly  cannot  have  more  vitality  than  the  animalculae 
themselves,  which  are  found  to  perish  by  the  slightest 
change  or  exposure.  And  admitting,  further,  that  such 
eggs  might  be  deposited  while  the  organic  matter  was 
transferring  to  the  phial,  why  do  they  generate  in  such 
swarms  throughout  the  matter  ?  Or  how  is  their  vitality 
preserved  after  that  matter  has  been  thrown  into  a  vessel 
of  boiling  water  and  immediately  corked  up  ?  These  cir- 
cumstances should  be  well  refuted  ;  for  they  bear  heavy 
against  the  egg  system.  Leuwenhock,  when  he  observed 
animalculae  in  the  sordes,  which  accumulates  about  teeth, 
resorted  to  the  opinion  that  they  themselves  are  transfer- 
red through  the  air,  water,  &c.  There  is  the  same  objec- 
tion in  this  case  as  in  the  foregoing  ;  and  this  naturalist 
was  not  guided  by  experimental  conviction  at  the  time  he 
advanced  the  opinion.  The  fact  turns  out,  when  we  ex- 
amine the  subject,  that  his  head  was  turned  about,  proving 
that  the  animalculae,  in  male  semen,  were  the  true  offspring 
in  miniature  ;  and  therefore  he  could  not  leave  it  to  be 
thought  by  the  world  that  his  favourite  theory  qualified  the 
mouth  for  foetal  generation.  He  accordingly  maintained, 
that  in  the  last  case,  animalculae  were  conveyed  by  eating 
or  drinking  rain  water,  he.  But  it  is  well  known  that 
persons  who  do  not  eat  cheese  have  them  also,  (or  the  re- 
verse) and  that  nothing  similar  to  them  is  found  to  exist  in 
rain  water.*  It  has  also  been  noticed,  as  a  proof  that 
regular  generation  takes  place  among  animalculae,  that  the 
paste-eel,  (a  species,)  when  cut  in  the  abdomen,  frequently 
gives  birth  to  numerous  young  eels.  This  fact,  however, 
does  not  in  the  least  account  for  their  first  appearance  in 
paste  under  the  circumstances  before  noticed.     All  that 

*  Barr's  Buffon  p.  189.  vol.  3. 
16 


122 

seems  proved,  is,  that  such  animalculee  have  also  the  power 
of  regular  generation ;  and  that,  heing  thus  more  perfect, 
there  is  a  greater  opening  for  the  equivocal  origin  of  vi- 
tality. 

Buffon  observes  that  when  blighted  corn  is  examined 
numerous  animalculse  are  observed  to  inhabit  its  sub- 
stance ;  and  seem  to  be  confined  altogether  in  their  pro- 
duction to  the  rotten  farina.  These  he  states  "may  be 
made  to  live  and  die  alternately,  and  as  often  as  we  please." 
And  further,  that  "  there  are  still  others,  even  in  great 
quantities,  which  are  at  first  kinds  of  vegetables,  afterwards 
become  species  of  animals,  then  return  again  to  vegeta- 
bles, and  so  alternately. w  This  naturalist  also  remarks 
that  '*  there  are,  perhaps,  as  many  beings,  either  living  or 
vegetating,  which  are  produced  by  the  fortuitous  assem- 
blage of  organic  molecules,  as  by  a  constant  and  suc- 
cessive generation."*  Yet  Buffon  supposed  that  he  thus 
proved  generation  never  to  be  equivocal ;  because  he 
considered  what  others  call  animalculae  or  small  ani- 
mals, to  be  nothing  more  than  moving  machines,  or  his 
own  living  organic  particles  which  death  never  destroyed. 
But  his  experiments  may  be  viewed  in  a  very  different 
light,  even  though  marshalled  to  support  a  very  improba- 
ble theory ;  for  whether  he  supposes  these  animalculae  to 
be  mere  moving  machines  or  not,  they  have  every  appear- 
ance of  animation.  Besides,  the  proof  given  by  assimila- 
tion, that  inanimate  mat;er  becomes  vital,  (apparently  in 
consequence  of  chemical  changes,  and  certainly  without 
the  regular  process  of  generation,)  we  may  add  that  from 
the  presence  of  worms  in  the  stomach  and  intestines.  It 
k&s    been  supposed  that  those    are   conveyed   in   without 

*Idejj)jVol.3.p.222, 


123 

food ;  but  is  not  this  as  badly  supported  as  any  ?  Inde- 
pendent of  the  implied  admission  by  medical  practitioners 
when  they  give  directions  not  to  consider  such  worms  as 
the  cause,  but  altogether  as  symptomatic  (which  is  literally 
nothing  else  than  the  effect)  of  disordered  digestion,  their 
origin  seems  proved  to  be  in  the  stomach  and  intestines, 
by  the  fact  that  no  such  worms  are  known  to  exist  out  of 
the  body,  and  instantly  perish  when  exposed.  They  are 
always  distinct  from  the  body,  and  only  appear  at  such 
times  and  places  as  indicate  the  greatest  latitude  to  che- 
mical combinations.  Why  do  they  not  oftener  manifest 
themselves  when  the  same  food  is  eaten  daily  ?  Particu- 
larly as  digestion  is  found  not  to  destroy  their  vitality.  In 
the  pustules  of  psora  (itch)  there  are  animalculae  as  well 
as  in  other  eruptions  ;  in  the  secretions  (as  semen)  and  in 
almost  all  animal  or  vegetable  fluids,  after  remaining  some 
time  at  rest  in  the  living  structure.  To  leave  animals, 
and  descend  :  we  meet  with  a  very  common  occurrence 
which  passe*  unnoticed  from  its  familiar  appearance  ;  I 
mean  the  formation  of  mould  in  a  dirty  tea  pot ;  or  on  the 
margin  of  vessels  holding  infusions.  We  can  hardly  sup- 
pose that  this  is  a  species  of  tea,  or  that  it  came  from 
China ;  yet  it  is  an  animated  production,  in  appearance 
similar  to  that  examined  by  Sir  Joseph  Banks.  But  it  is 
needless  to  examine  the  subject  further.  There  are  che- 
mical changes  always  antecedent  to  the  appearance  of 
these  animated  productions  ;  so  there  are  in  assimilation, 
The  materials  are  the  same,  as  well  as  most  of  the  agents  . 
regular  generation  seems  throughout  to  be  but  a  process 
of  assimilation  ;  first,  in  the  ovaria,  to  form  the  embryo, 
(as  other  living  and  definite  structure  of  the  female  is 
formed.)  then  in  the  uterus,  aided  stili  by  the  female  ;  or 
independently  of  all  connexion,  as  in  eggs  and  seeds.  Thf 


124 

great  obstacle  to  fortuitous  generation  must,  therefore,  be 
the  process  of  assimilation  ;  for  when  this  succeeds,  a  fluid 
will  be  produced  capable  of  forming  a  vital  circulating 
structure,  (as  blood  vessels,)  particularly  as  there  appears 
no  necessity  for  a  complex  system  to  support  animation, 
Plants,  seeds,  embryos,  and  the  imperfect  classes  of  ani- 
mals show,  that  the  process  is  not  always  the  same ;  and 
that  it  is  equally  effectual  when  curtailed  of  the  principle 
features  which  characterize  it  in  adults.  The  generating 
fluid  (similar  to  blood)  is  manifestly  proved  by  these  ex- 
amples to  be  of  different  natures  ;  so  that  it  is  impossible 
to  foresay  what  its  origin  must  always  be  in  a  living  body* 
As  to  the  objection  of  final  ends,  we  are  as  much  at  a  loss 
in  one  case  as  the  other.  The  animalculae  and  worms 
seem  equally  useless  in  the  living  fluids,  whether  brought 
to  life  by  regular  or  fortuitous  generation  ;  and  the  fact  is 
well  known,  that  as  we  descend  and  examine  the  power 
and  process  of  generation  in  the  lower  classes  of  animals, 
we  find  the  most  astonishing  deviations  from  the  common 
form.  Sexes  do  not  appear  necessary  for  the  procreation  of 
a  polypus,  which  gives  birth  to  new  ones  by  simple  division  | 
or  to  those  animated  creatures  who  generate  by  shed- 
ding a  limb.  In  these  cases  living  systems  are  formed,  (inde- 
pendently of  any  connexion)  in  parts,  which  previously 
seemed  dependent  members ;  and  they  prove  that  the 
simplest  structure  is  sufficient  to  support  such  system. 
Further,  we  should  reflect  that  animation  is  founded  upon 
irritabillity,  which  seems  nothing  more  than  a  property  of 
matter  depending  upon  the  action  or  influence  of  stimuli, 
on  an  indefinite  structure  and  composition.  Before  the 
application  of  a  stimulus  we  have  not  the  slighest  evidence 
of  irritability,  (and  indeed  it  seems  impossible  by  any 
other  means  to   prove    it ;)   hence   it  is  the  matter  which 


125 

qualifies  the  existence  of  animation  more  than  the  process 
of  generation.  Other  circumstances  in  the  regular  pro- 
cess do  undoubtedly  exist,  for  which  it  would  be  presump- 
tion (at  the  present  imperfect  state  of  knowledge)  to 
give  such  a  rationale  ;  but  the  object  is  merely  to  examine 
the  outline  or  rather  the  nature  of  one  of  its  principles. 
In  the  pursuit  of  truth  we  should  rely  upon  facts  more 
than  opinion ;  for  the  last  never  can  unfold  the  woiks  of 
God,  or  manifest  His  wisdom,  whereas  the  first  are  always 
illustrative.  The  ancients  admitted  the  fact  of  fortuitous 
generation,  and  quietly  established  the  maxim,  "  corruptio 
unius,  generatio  alterius  ;"  but  after  the  discovery  of  ani- 
malculse  in  serum,  by  Leuwenhock,  philosophers  became 
warm  with  contention.  This  naturalist,  after  several  times 
retracting  his  opinions,  maintained  them  to  be  embryos  in 
miniature,  Buffon  on  the  other  hand  opposed  Leuwen- 
hock, by  contending  that  they  were  nothing  less  than  his 
immutable  but  fanciful,  "  living  organic  particles  ;"  while 
Needham  had  the  boldness  to  suppose  their  origin  to  be 
equivocal,  or  resulting  from  material  laws,  independent  of 
regular  generation.  These  opinions  had  a  fashionable  ex- 
istence, and  then  subsided,  leaving  but  little  taste  for  fur- 
ther inquiry.  But  notwithstanding  such  opposite  views, 
the  facts  noticed  by  these  philosophers  became  the  more 
confirmed,  and  must  still  continue  to  exist,  unless  nature 
forgets  herself  so  far  as  to  overturn  her  present  regula- 
tions. I  shall  close  this  essay  without  drawing  a  single 
conclusion,  persuaded  that  the  facts  must  answer  for 
themselves. 


FIKIS. 


COL 

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